Newborn mouse DNA was digested with a restriction endonuclease EcoRI and concentrated with respect to ribosomal RNA sequences by an RPC-5 column.DNA fragments of 14-17 kilobases in length, most probably containing promoter region of the ribosomal RNA gene, were used for cloning with λgt WES•λB as a vector using an in vitro packaging technique. Several clones containing 18S rRNA sequences were obtained. One of the clones which was transferred to a plasmid pBR322 (designated as pMrEL-1) was 14 kilobases in length, having only a part of 18S rRNA sequence. These results strongly suggest that this fragment carries a promoter region of the ribosomal RNA gene.
We report here the molecular cloning and sequence analysis of DNAs complementary to mRNAs for myosin alkali light chain of chicken embryo and adult leg skeletal muscle. pSMA2-1 contained an 818 base-pair insert that includes the entire coding region and 5' and 3' untranslated regions of A2 mRNA. pSMA1-1 contained a 848 base-pair insert that included the 3' untranslated region and almost all of the coding region except for the N-terminal 13 amino acid residues of the A1 light chain. The 741 nucleotide sequences of A1 and A2 mRNAs corresponding to C-terminal 141 amino acid residues and 3' untranslated regions were identical. The 5' terminal nucleotide sequences corresponding to N-terminal 35 amino acid residues of A1 chain were quite different from the sequences corresponding to N-terminal 8 amino acid residues and of the 5' untranslated region of A2 mRNA. These findings are discussed in relation to the structures of the genes for A1 and A2 mRNA.
