La mentira, una reivindicación moral. De cómo la mentira es útil en un paciente en etapa terminal / The lie, a moral claim. How lying is useful in a terminally ill patient

Resumen: La mentira es considerada un antivalor moral, siempre tiene una connotación negativa. Sin embargo, su uso está muy extendido desde el punto de vista biológico como mecanismo de supervivencia y en el ser humano incluso desde el punto de vista de integración social. El autoengaño, considerado una manifestación suprema del uso humano de la mentira, tiene estrecha relación con la generación de optimismo y esperanza, las personas con problemas para integrar un autoengaño tienen con más frecuencia alteraciones patológicas en el estado de ánimo, sobre todo depresión. Este artículo analiza desde algunos puntos de vista ético-filosóficos las ventajas y desventajas del uso de la mentira para promover el autoengaño en pacientes con enfermedad terminal.

Abstract: The lie is considered a moral flaw, always has a negative connotation. Nevertheless its use is very extended from the biological point of view as mechanism of survival and in the human being, even from the point of view of social integration. Self-deception, considered a supreme manifestation of the human use of lies, is closely related to the generation of optimism and hope, people with problems to integrate self-deception have more frequently pathological alterations in mood, especially depression. The advantages and disadvantages of the use of lying to promote self-deception in patients with terminal illness are analyzed from some ethical-philosophical points of view.

Recognition of a human arrest site is conserved between RNA polymerase II and prokaryotic RNA polymerases.

DNA sequences that arrest transcription by either eukaryotic RNA polymerase II or Escherichia coli RNA polymerase have been identified previously. Elongation factors SII and GreB are RNA polymerase-binding proteins that enable readthrough of arrest sites by these enzymes, respectively. This functional similarity has led to general models of elongation applicable to both eukaryotic and prokaryotic enzymes. Here we have transcribed with phage and bacterial RNA polymerases, a human DNA sequence previously defined as an arrest site for RNA polymerase II. The phage and bacterial enzymes both respond efficiently to the arrest signal in vitro at limiting levels of nucleoside triphosphates. The E. coli polymerase remains in a template-engaged complex for many hours, can be isolated, and is potentially active. The enzyme displays a relatively slow first-order loss of elongation competence as it dwells at the arrest site. Bacterial RNA polymerase arrested at the human site is reactivated by GreB in the same way that RNA polymerase II arrested at this site is stimulated by SII. Very efficient readthrough can be achieved by phage, bacterial, and eukaryotic RNA polymerases in the absence of elongation factors if 5-Br-UTP is substituted for UTP. These findings provide additional and direct evidence for functional similarity between prokaryotic and eukaryotic transcription elongation and readthrough mechanisms.

A DNA minor groove-binding ligand both potentiates and arrests transcription by RNA polymerase II. Elongation factor SII enables readthrough at arrest sites.

RNA polymerase II encounters various obstacles to transcript elongation both in vivo and in vitro. These include DNA sequence elements and protein bound to the major groove of DNA. Elongation factor SII binds to RNA polymerase II and enables the enzyme to bypass these impediments. SII also activates nascent RNA cleavage by the arrested transcription elongation complex, an activity intimately involved in the readthrough process. Here we identify another type of reversible blockage to RNA polymerase II transcription, the antitumor antibiotic distamycin, which binds in the minor groove of A + T-rich DNA. SII facilitates readthrough of arrest sites resulting from DNA-binding of the drug. In response to SII, these complexes cleave their nascent RNA chains. These findings confirm that SII is a general elongation factor that potentiates transcription through a variety of impediments. They also strengthen the idea that SII stimulates transcription by activating nascent RNA cleavage. In some cases, distamycin can potentiate transcription through a naturally occurring pause site. We also show that the template undergoes a conformational change in the presence of distamycin. This suggests that distamycin can transform DNA from an elongation-non-permissive configuration into an elongation-permissive form and we take this as independent evidence confirming that DNA structure influences transcription elongation by RNA polymerase II.

Nascent RNA cleavage by arrested RNA polymerase II does not require upstream translocation of the elongation complex on DNA.

Obstacles incurred by RNA polymerase II during primary transcript synthesis have been identified in vivo and in vitro. Transcription past these impediments requires SII, an RNA polymerase II-binding protein. SII also activates a nuclease in arrested elongation complexes and this nascent RNA shortening precedes transcriptional readthrough. Here we show that in the presence of SII and nucleotides, transcript cleavage is detected during SII-dependent elongation but not during SII-independent transcription. Thus, under typical transcription conditions, SII is necessary but insufficient to activate RNA cleavage. RNA cleavage could serve to move RNA polymerase II away from the transcriptional impediment and/or permit RNA polymerase II multiple attempts at RNA elongation. By mapping the positions of the 3'-ends of RNAs and the elongation complex on DNA, we demonstrate that upstream movement of RNA polymerase II is not required for limited RNA shortening (seven to nine nucleotides) and reactivation of an arrested complex. Arrested complexes become elongation competent after removal of no more than nine nucleotides from the nascent RNA's 3'-end. Further cleavage of nascent RNA, however, does result in "backward" translocation of the enzyme. We also show that one round of RNA cleavage is insufficient for full readthrough at an arrest site, consistent with a previously suggested mechanism of SII action.

Elongation factor SII-dependent transcription by RNA polymerase II through a sequence-specific DNA-binding protein.

In eukaryotes the genetic material is contained within a coiled, protein-coated structure known as chromatin. RNA polymerases must recognize specific nucleoprotein assemblies and maintain contact with the underlying DNA duplex for many thousands of base pairs. Template-bound lac operon repressor from Escherichia coli arrests RNA polymerase II in vitro and in vivo [Kuhn, A., Bartsch, I. & Grummt, I. (1990) Nature (London) 344, 559-562; Deuschele, U., Hipskind, R. A. & Bujard, H. (1990) Science 248, 480-483]. We show that in a reconstituted transcription system, elongation factor SII enables RNA polymerase II to proceed through this blockage at high efficiency. lac repressor-arrested elongation complexes display an SII-activated transcript cleavage reaction, an activity associated with transcriptional read-through of a previously characterized region of bent DNA. This demonstrates factor-dependent transcription by RNA polymerase II through a sequence-specific DNA-binding protein. Nascent transcript cleavage may be a general mechanism by which RNA polymerase II can bypass many transcriptional impediments.

Transcription elongation by RNA polymerase II: mechanism of SII activation.

RNA chain elongation by RNA polymerase is a dynamic process. Techniques that allow the isolation of active elongation complexes have enabled investigators to describe individual steps in the polymerization of RNA chains. This article will describe recent studies of elongation by RNA polymerase II (pol II). At least four types of blockage to chain elongation can be overcome by elongation factor SII: (a) naturally occurring "arrest" sequences, (b) DNA-bound protein, (c) drugs bound in the DNA minor groove, and (d) chain-terminating substrates incorporated into the RNA chain. SII binds to RNA polymerase II and stimulates a ribonuclease activity that shortens nascent transcripts from their 3' ends. This RNA cleavage is required for chain elongation from some template positions. As a result, the pol II elongation complex can repeatedly shorten and reextend the nascent RNA chain in a process we refer to as cleavage-resynthesis. Hence, assembly of large RNAs does not necessarily proceed in a direct manner. The ability to shorten and reextend nascent RNAs means that a transcription impediment through which only half the enzyme molecules can proceed per encounter, can be overcome by 99% of the molecules after six iterations of cleavage-resynthesis. Surprisingly, the boundaries of the elongation complex do not move upstream after RNA cleavage. The physico-chemical alterations in the elongation complex that accompany RNA cleavage and permit renewed chain elongation are not yet understood.

The RNA polymerase II elongation complex. Factor-dependent transcription elongation involves nascent RNA cleavage.

Regulation of transcription elongation is an important mechanism in controlling eukaryotic gene expression. SII is an RNA polymerase II-binding protein that stimulates transcription elongation and also activates nascent transcript cleavage by RNA polymerase II in elongation complexes in vitro (Reines, D. (1992) J. Biol. Chem. 267, 3795-3800). Here we show that SII-dependent in vitro transcription through an arrest site in a human gene is preceded by nascent transcript cleavage. RNA cleavage appeared to be an obligatory step in the SII activation process. Recombinant SII activated cleavage while a truncated derivative lacking polymerase binding activity did not. Cleavage was not restricted to an elongation complex arrested at this particular site, showing that nascent RNA hydrolysis is a general property of RNA polymerase II elongation complexes. These data support a model whereby SII stimulates elongation via a ribonuclease activity of the elongation complex.

Tissue-specific expression phenotypes of Hawaiian Drosophila Adh genes in Drosophila melanogaster transformants.

Interspecific differences in the tissue-specific patterns of expression displayed by the alcohol dehydrogenase (Adh) genes within the Hawaiian picture-winged Drosophila represent a rich source of evolutionary variation in gene regulation. Study of the cis-acting elements responsible for regulatory differences between Adh genes from various species is greatly facilitated by analyzing the behavior of the different Adh genes in a homogeneous background. Accordingly, the Adh gene from Drosophila grimshawi was introduced into the germ line of Drosophila melanogaster by means of P element-mediated transformation, and transformants carrying this gene were compared to transformants carrying the Adh genes from Drosophila affinidisjuncta and Drosophila hawaiiensis. The results indicate that the D. affinidisjuncta and D. grimshawi genes have relatively higher levels of expression and broader tissue distribution of expression than the D. hawaiiensis gene in larvae. All three genes are expressed at similar overall levels in adults, with differences in tissue distribution of enzyme activity corresponding to the pattern in the donor species. However, certain systematic differences between Adh gene expression in transformants and in the Hawaiian Drosophila are noted along with tissue-specific position effects in some cases. The implications of these findings for the understanding of evolved regulatory variation are discussed.