An element downstream of the cap site is required for transcription of the gene encoding mouse ribosomal protein L32

To identify the elements that regulate transcription of the mouse gene encoding ribosomal protein L32 (rpL32), we transfected monkey kidney (COS or CV-1) cells with mutants bearing progressive 5' deletions or an internal deletion in exon I and measured their transient expression by S1 nuclease protection analysis. When the mutant genes were tested in the vector pi SVHSplac, which contains a short segment of the oriregion of simian virus 40, maximum expression was observed with as little as 36 base pairs of 5' flanking sequence, and the mutant bearing the exon I deletion was expressed very efficiently. However, when the genes were tested in a simple prokaryotic (pUC) vector, the expression was increased 3- to 4-fold by sequences between -36 and -159, and the exon I segment was absolutely required for expression. Gel mobility-shift and methylation interference analyses revealed that a nuclear factor specifically binds to a GGCTGCCATC sequence within this exon I segment. These results, taken together with other recent findings, indicate that the elements involved in transcriptional regulation of the rpL32 gene are distributed over a 200-base-pair region that spans the cap site. The contributions of some of these elements are apparently masked in the presence of simian virus 40 ori-region elements.