Regulated Expression of Nuclear Protein(s) in Myogenic Cells- That Binds to a Conserved 3′ Untranslated Region in Proαl(I) Collagen cDNA

Abstract

We describe the identification and DNA-binding properties of nuclear proteins from rat L6 myoblasts which recognize an interspecies conserved 3′ untranslated segment of proα1(I) collagen cDNA. Levels of the two proα1(I) collagen RNAs, present in L6 myoblasts, decreased drastically between 54 and 75 h after induction of myotube formation in serum-free medium. Both mRNAs contained a conserved sequence segment of 135 nucleotides (termed tame sequence) in the 3′ untranslated region that had 96% homology to the human and murine proα1(I) collagen genes. The cDNA of this tame sequence was specifically recognized by nuclear protein(s) from L6 myoblasts, as judged by gel retardation assays and DNase I footprints. The tame-binding protein(s) was able to recognize its target sequence on double-stranded DNA but bound also to the appropriate single-stranded oligonucleotide. Protein that bound to the tame sequence was undetectable in nuclear extracts of L6 myotubes that did not accumulate the two collagen mRNAs. Therefore, the activity of this nuclear protein seems to be linked to accumulation of the sequences that it recognizes in vitro. The collagen RNAs and the nuclear tame-binding proteins reappeared after a change of medium, which further suggests that the RNAs and the protein(s) are coordinately regulated.