Chromosomal proteins HMG-14 and HMG-17. Distinct multigene families coding for similar types of transcripts

Human nonhistone chromosomal proteins HMG-14 and HMG-17 are encoded by genes which are part of multigene families. Southern analysis of human, mouse, and rat genomic restriction digests reveals that the two families are distinct. Although the cDNAs of HMG-14 and HMG-17 do not cross-hybridize, they have several similar structural features: the open reading frame comprises only 23% of the transcripts, the 5'-untranslated region is extremely GC rich whereas the 3'-untranslated region is unusually long and AT rich. The overall sequence homology between the two transcripts is highest (71%) in the 90 nucleotides coding for the DNA-binding domains of the proteins. The sequence of the human HMG-14 and HMG-17 proteins, deduced from the open reading frame, differs by more than 50%; the DNA-binding domains of the proteins show 74% sequence homology. However, even in this 30-residue long peptide there are significant differences between the proteins as the proline content of HMG-17 (8 residues) is twice that of HMG-14. The two proteins have different hydropathy index profiles and are serologically distinct. The multigene families may have evolved independently from similar genetic elements or from a shared ancestral gene in which the nucleotide sequence coding for the DNA-binding domain of the protein is the most conserved region. The structural differences between the molecules and the differences in their DNA-binding domains suggest that the proteins may be involved in distinguishable cellular functions.