MOLECULAR-CLONING OF THE CDNA-ENCODING A HELIX-LOOP-HELIX PROTEIN, MOUSE ID1B - TISSUE-SPECIFIC EXPRESSION OF ID1A AND ID1B GENES

A cDNA encoding a 168 amino acid mouse ID1B helix-loop-helix protein, the longest among the ID family of proteins so far identified, was clo ned and its nucleotide sequence determined. Mouse ID1B mRNA is disting uishable from the mRNA encoding ID1A at its 3' end, and the relative l evel of expression of these two different mRNAs is similar in most tis sues, with exception of skeletal muscle and kidney. Comparison of the most carboxyl terminal predicted amino acid sequences of ID1 proteins reveals 100% identity for ID1A, but the predicted Id1B proteins of sev eral species are different.