Secretin is an endocrine hormone that stimulates the secretion of bicarbonate-rich pancreatic fluids. Recently, it has been discussed that secretin deficiency may be implicated in autistic syndrome, suggesting that the hormone could have a neuroendocrine function in addition to its role in digestion. In the present study, the human secretin gene (SCT) was isolated from a bacterial artificial chromosome genomic library. SCT contains four exons, with the protein coding regions spanning 713 bp of genomic DNA. Human SCT is similar structurally to the secretin genes of other species. Amino acid conservation, however, is most pronounced within the exon encoding the biologically active mature peptide. Northern blot analysis shows that human SCT transcripts are located in the spleen, intestinal tract, and brain. Radiation hybrid mapping places the SCT locus on chromosome 11p15.5.

We previously demonstrated that when nonretroviral RNAs are encapsidated in retroviral particles they can be reverse transcribed into cDNAs, which are then integrated into the cellular genome. This transfer of genetic information via retroviral infection has been designated retrofection. Further analyses of three genes transferred in this manner (retrogenes) Several systems have been developed to study the recombination events that result in the acquisition of transferred genes by host cells (9,12,30,41,43); these systems primarily utilize transfection or microinjection to deliver the gene of interest to the host cell. Genes transferred in these ways, however, are frequently integrated as tandem arrays or in multiple sites. More, recently, we and others described systems that allow the study of the integration and expression of single-copy genes (10,22). These studies entail infection of tissue culture cells with retroviral particles containing nonretroviral RNAs and authentic (virally encoded) reverse transcriptase, a process we have called retrofection. In our system (Fig. 1) that harbor single-copy neo genes integrated into the chromosome. This process is RNA mediated and does not appear to require any retroviral sequences in cis, although inclusion of retroviral sequences increases retrofection efficiency.DNA sequences occasionally appear in new genomic locations, both in germ line and somatic cells. In many instances, there is good evidence that these molecules (including certain retrotransposons such as long interspersed nuclear elements and intracisternal A particles) have transposed via RNA intermediates (1). Structural similarities between many of these genes and processed pseudogenes, including the lack of functional transcriptional control sequences and the presence of 3'-terminal poly(dA), have led to the suggestion that processed pseudogenes arose by the integration of cDNAs produced by reverse transcription (39, 49). To evaluate this suggestion and to study the processes involved in the retrovirally mediated transfer of nonretroviral genes, we cloned and sequenced neo retrogenes from three independently derived G418-resistant QT35 clones. Fig. 1). In the case of the mass G418r cultures described in Table 1 and Fig. 7

Swi6 associates with Swi4 to activate HO and many other late G 1 -specific transcripts in budding yeast. Genetic screens for suppressors of SWI6 mutants have been carried out. A total of 112 of these mutants have been identified and most fall into seven complementation groups. Six of these genes have been cloned and identified and they all encode subunits of the mediator complex. These mutants restore transcription to the HO-lacZ reporter in the absence of Swi6 and have variable effects on other Swi6 target genes. Deletions of other nonessential mediator components have been tested directly for suppression of, or genetic interaction with, swi6. Mutations in half of the known subunits of mediator show suppression and/or growth defects in combination with swi6. These phenotypes are highly variable and do not correlate with a specific module of the mediator. Mutations in tail module components sin4 and pgd1 showed both growth defects and suppression when combined with swi6, but a third tail component, gal11, showed neither. A truncated form of the essential Srb7 mediator subunit also suppresses swi6 mutations and shows a defect in recruitment of the tail module components Sin4, Pgd1, and Gal11 to the mediator complex.

We previously demonstrated that when nonretroviral RNAs are encapsidated in retroviral particles they can be reverse transcribed into cDNAs, which are then integrated into the cellular genome. This transfer of genetic information via retroviral infection has been designated retrofection. Further analyses of three genes transferred in this manner (retrogenes) revealed that each was present in a single copy at a different site in the recipient quail cell genome and included a transcriptional promoter encoded by the encapsidated neo RNA. A unique feature of the retrogenes was a common 16-nucleotide sequence at or near a recombination border, which was not present in either recombination partner. The existence of this sequence suggests a common mechanism of retrogene formation and/or integration mediated by retrofection.