Expression of the gene for hematopoietic cell specific protein is not restricted to cells of hematopoietic origin.

Hematopoietic cell line specific protein (HS1) is an intracellular signaling protein that has been reported as specifically expressed in hematopoietic cells. HS1 is known as a major substrate of protein-tyrosine kinases following activation by B-cell or T-cell receptor complexes. We report the first evidence that HS1 is also expressed in a variety of tissues different from hematopoietic tissues by using sensitive expression analysis including real-time quantitative RT-PCR. While former studies on HS1-expression were mostly limited to cells of hematopoietic origin, we screened a larger number of human tissues including tumor samples. Normal lung tissue showed a high degree of HS1 expression, second to the expression of hematopoietic cells. Expression of HS1 in tumor tissues was also clearly detectable. Our findings suggest that the signaling protein HS1 is involved in pathways different from the ones that have a specific role in the intracellular processes of hematopoietic cells.

The human L1 promoter: variable transcription initiation sites and a major impact of upstream flanking sequence on promoter activity.

Human L1 elements are non-LTR retrotransposons that comprise approximately 17% of the human genome. Their 5'-untranslated region (5'-UTR) serves as a promoter for L1 transcription. Now we find that transcription initiation sites are not restricted to nucleotide +1 but vary considerably in both downstream and upstream directions. Transcription initiating upstream explains additional nucleotides often seen between the 5'-target site duplication and the L1 start site. A higher frequency of G nucleotides observed upstream from the L1 can be explained by reverse transcription of the L1 RNA 5'-CAP, which is further supported by extra Gs seen for full-length HERV-W pseudogenes. We assayed 5'-UTR promoter activities for several full-length human L1 elements, and found that upstream flanking cellular sequences strongly influence the L1 5'-UTR promoter. These sequences either repress or enhance the L1 promoter activity. Therefore, the evolutionary success of a human L1 in producing progeny depends not only on the L1 itself, but also on its genomic integration site. The promoter mechanism of L1 is reminiscent of initiator (Inr) elements that are TATA-less promoters expressing several cellular genes. We suggest that the L1 5'-UTR is able to form an Inr element that reaches into upstream flanking sequence.

Presence of dUTPase in the various human endogenous retrovirus K (HERV-K) families.

Various retroviruses have been shown to encode dUTPase. The overall phylogeny of dUTPase is unclear, though. The human genome contains a significant amount of human endogenous retroviruses (HERV) representing fossilized sequences of ancient exogenous retroviruses. A few HERV families have been reported to harbor dUTPase domains. We surveyed the various HERV families for the presence of dUTPase and found that ancestors of all HERV-K families but one encoded dUTPase. With two exceptions phylogenetic analysis shows a monophyletic origin of dUTPase for the different HERV-K dUTPases. Sequences of consensus dUTPase domains suggest that the various exogenous ancestors of HERV-K once encoded active enzymes. Our analysis provides informations on dUTPase phylogeny and further shows that endogenous retroviruses provide important informations regarding retrovirus evolution.

The human endogenous retrovirus family HERV-K(HML-3).

A substantial amount of the human genome is composed of human endogenous retroviruses (HERVs). Manifold HERV families have been identified, among them several so-called HERV-K(HML) families. Although the HERV-K(HML-2) family has been studied in detail, other HERV-K families are not as well characterized. We describe here the HERV-K HML-3 family in more detail. We estimate that there are about 140 proviral loci or remains of such per haploid genome. Most loci are severely mutated. Proviruses displaying larger deletions in gag and pol are common. A multiple alignment of 73 HERV-K(HML-3) sequences displays several potentially important differences compared with the HERVK9I sequence in Repbase. A consensus sequence with open reading frames for all retroviral genes was generated, for which intact dUTPase motifs and env gene variants with different coding capacities are observed. Phylogenetic analysis shows near-monophyly with distinction of two closely related subgroups. Proviruses formed about 36 million years ago. However, no continuous activity through primate evolution is indicated.