Genomic and cDNA structures of the gene encoding the chicken ZF5 DNA binding protein.

Genomic and cDNA clones encoding the chicken ZF5 transcription factor were isolated and sequenced. Conceptual translation of the cDNAs indicates that chicken ZF5 has five zinc fingers at its C-terminal end and a POZ/BTB protein-interaction domain at its N-terminal end. These two functional domains are more than 99% identical in amino acid sequence between the chicken and mouse proteins, whereas the region separating the POZ/BTB and DNA binding domains is only 74% identical. The entire 458 amino acid open reading frame is contained within a single exon, except for the initiator methionine codon which alone is supplied from an upstream exon by mRNA splicing.

Identification of proximal sequence element nucleotides contributing to the differential expression of variant U4 small nuclear RNA genes.

The two U4 genes in the chicken genome code for distinct sequence variants of U4 small nuclear RNA that are differentially expressed during development. Whereas U4B RNA is constitutively expressed, U4X RNA is specifically down-regulated relative to U4B in a tissue-specific manner during development. To investigate mechanisms controlling the differential expression of the U4B and U4X genes, chimeric U4 genes were constructed and their transcriptional activities assayed by injection into Xenopus oocytes or by transfection of CV-1 cells. The proximal regulatory region of the U4B gene and the enhancers of both the U4B and U4X genes functioned efficiently in each expression system. However, the proximal region of the U4X gene was inactive. To localize and identify the responsible nucleotides, reciprocal point mutations were introduced into the U4X and U4B proximal regulatory regions. The results indicate that the U4X gene contains a suboptimal proximal sequence element, and that this results primarily from the identities of the nucleotides at positions -61 and -57 relative to the transcription start site.