Cloning and expression in Escherichia coli of a gene, hup, encoding the histone-like protein HU of Bifidobacterium longum

A genomic DNA library of Bifidobacterium longum ATCC15707 was transfected into an Escherichia coli strain deficient in both HU and IHF, the growth of which is cold-sensitive because of the deficiency in these proteins. Cold-resistant colonies were selected and the DNA was cloned and sequenced. A polypeptide consisted of 93 amino acids, a predicted molecular mass of 9983 Da with an isoelectric point of 10.35, was deduced from an orf in the middle of the DNA fragment. The amino acid sequence was highly similar to HU family proteins, and 26 aas of N terminal was identical to a histone-like protein, HBI, a HU family protein of B. longum. Incapabilities of Mu phage propagation in an E. coli mutant deficient in HU or IHF could be suppressed by DNA bearing this orf. These results showed that the orf is a gene hup encoding HBI, a histone-like protein HU of B. longum.