Structure of the gene encoding the ubiquitin-conjugating enzyme Ubcm4, characterization of its promoter, and chromosomal location

Ubiquitin-conjugating enzymes (E2 or Ubc) play a key role in the post- translational modification of proteins by ubiquitylation. They are encoded by a large family of genes that are closely related to each other. In this paper we present the first complete structural analysis, including the promoter and the chromosomal location, of a member of this family, the mouse Ubcm4 gene. At the genomic level the Ubcm4 gene spans approx. 50 kb and is composed of four exons. Only about 1% of the total gene codes for amino acids. The four different Ubcm4 specific RNAs encode the same protein and differ only in the length of the 3' untranslated region. The polyadenylation signals used by the four different RNAs are all within the 3' terminal exon. At the 5' end of the gene, multiple transcriptional start sites were mapped within a region of 25 bp. The region proximal to the initiation sites does not contain a TATA box and is not GC-rich. Transient chloramphenicol acetyltransferase assays, however, showed that this region can promote the expression of a reporter gene and that 15 bp upstream of the first initiation site were sufficient for basal expression. The Ubcm4 gene was mapped by interspecific backcross analysis to the proximal region of mouse chromosome 16.