Evaluation of captive gibbons (Hylobates spp., Nomascus spp., Symphalangus spp.) in North American Zoological Institutions for Gibbon Ape Leukemia Virus (GALV).

This study evaluated 79 captive gibbons (Hylobates, Nomascus, and Symphalangus spp.) within 30 North American zoological institutions for evidence of exposure to and possible infection with gibbon ape leukemia virus (GALV). Enzyme-linked immunosorbent assays (ELISAs) on gibbon serum samples revealed the presence of antibodies against GALV antigens in 28% of animals, indicating previous exposure or possibly protective immunity to GALV. Virus detection in gibbon blood or serum using polymerase chain reaction (PCR) or co-culture of gibbon peripheral blood mononuclear cells with human cells was negative for all samples submitted. The majority (19/27, 70%) of animals with reported health conditions were clinically healthy at the time of sample collection. Historically accrued clinical data were used to assess association of diseases in gibbons antibody positive for GALV. The results suggest captive gibbons could mount an immune response to GALV and show no evidence of infection. There was no association with neoplastic conditions in seropositive animals. The potential role of gibbons as a reservoir for GALV and the role of GALV as an epizoonotic-zoonotic agent or as a contributor to gibbon ape morbidity and mortality are not substantiated by the study findings.

Testing constraints on rRNA bases that make nonsequence-specific contacts with the codon-anticodon complex in the ribosomal A site.

During protein synthesis, interactions between the decoding center of the ribosome and the codon-anticodon complexes maintain translation accuracy. Correct aminoacyl-tRNAs induce the ribosome to shift into a "closed" conformation that both blocks tRNA dissociation and accelerates the process of tRNA acceptance. As part of the ribosomal recognition of cognate tRNAs, the rRNA nucleotides G530 and A1492 form a hydrogen-bonded pair that interacts with the middle position of the codon.anticodon complex and recognizes correct Watson-Crick base pairs. Exchanging these two nucleotides (A530 and G1492) would not disrupt these interactions, suggesting that such a double mutant ribosome might properly recognize tRNAs and support viability. We find, however, that exchange mutants retain little ribosomal activity. We suggest that even though the exchanged nucleotides might function properly during tRNA recruitment, they might disrupt one or more other functions of the nucleotides during other stages of protein synthesis.

An mRNA sequence derived from the yeast EST3 gene stimulates programmed +1 translational frameshifting.

Programmed translational frameshift sites are sequences in mRNAs that promote frequent stochastic changes in translational reading frame allowing expression of alternative forms of protein products. The EST3 gene of Saccharomyces cerevisiae, encoding a subunit of telomerase, uses a programmed +1 frameshift site in its expression. We show that the site is complex, consisting of a heptameric sequence at which the frameshift occurs and a downstream 27-nucleotide stimulator sequence that increases frameshifting eightfold. The stimulator appears to be modular, composed of at least three separable domains. It increases frameshifting only when ribosomes pause at the frameshift site because of a limiting supply of a cognate aminoacyl-tRNA and not when pausing occurs at a nonsense codon. These data suggest that the EST3 stimulator may modulate access by aminoacyl-tRNAs to the ribosomal A site by interacting with several targets in a ribosome paused during elongation.

An mRNA sequence derived from a programmed frameshifting signal decreases codon discrimination during translation initiation.

Sequences and structures in the mRNA can alter the accuracy of translation. In some cases, mRNA secondary structures like hairpin loops or pseudoknots can cause frequent errors of translational reading frame (programmed frameshifting) or misreading of termination codons as sense (nonsense readthrough). In other cases, the primary mRNA sequence stimulates the error probably by interacting with an element of the ribosome to interfere with error correction. One such primary mRNA sequence, the Ty3 stimulator, increases programmed +1 frameshifting 7.5 times in the yeast Saccharomyces cerevisiae. Here we show that this stimulator also increases the usage of non-AUG initiation codons in the bacterium Escherichia coli but not in S. cerevisiae. These data suggest that in E. coli, though not in yeast, an element of the ribosome's elongation accuracy mechanism ensures initiation accuracy.