Duplicated NHP6 genes of Saccharomyces cerevisiae encode proteins homologous to bovine high mobility group protein 1

The nonhistone chromosomal protein NHP6 from Saccharomyces cerevisiae has been previously isolated and its amino-terminal sequence determined. In this report, synthetic oligonucleotides, designed from the limited NHP6 amino acid sequence, were used as hybridization probes to clone the NHP6A gene from a yeast genomic library. Low stringency Southern blot analysis showed that there was a second gene homologous to NHP6A. This gene, NHP6B, was also cloned and sequenced. Nucleotide sequence analysis revealed that NHP6B has six extra amino acids at its amino terminus, but that NHP6A and NHP6B match at 87% of the rest of their sequences. S1 nuclease analysis was used to show that both genes are transcribed; the major transcription start sites lie 30 bases before the first ATG codon. Interestingly, the ~ 11-kDa NHP6A and NHP6B proteins are homologous to the middle segment of the 27-kDa chromatin-associated high mobility group protein 1 from calf; NHP6A and NHP6B each have over 40% identity with this part of high mobility group protein 1. Possible functions for the NHP6 proteins are discussed in light of this homology.