2) is essential. Mycobacterium smegmatis is unique among Mycobacteria in having
a third chaperonin gene, cpn60.3. The cpn60.1 gene has a gene upstream (cpn10) that is homologous to the gene for the E. coli co-chaperonin GroES. Phylogenetic analysis of the mycobacterial homologues suggests that early gene duplication and sequence divergence gave rise to the cpn60.1 and cpn60.2 genes found in all Mycobacteria species, while cpn60.3 appears to have been acquired by horizontal gene transfer. Here, we show that cpn60.2 and cpn10 are expressed more strongly than cpn60.1, while learn more cpn60.3 shows very low levels of expression. The expression of all the genes, except cpn60.3, is significantly induced by heat shock, but much less so by other stresses. We mapped mRNA 5′-ends for the cpn10 and cpn60.1 genes, and measured the promoter activity of the upstream regions of both genes. The results show that the mRNA for this operon is cleaved between the cpn10 and cpn60.1 genes. These results are consistent with the evolution of a distinct function for the cpn60.1 gene. Protein structures are fully determined by their Lumacaftor amino acid sequences
(Anfinsen, 1973). However, in vivo, molecular chaperones are required to assist the folding of many proteins to their native state under normal conditions, where a high protein concentration can lead to aggregation unless transiently exposed hydrophobic regions are protected (Lin & Rye, 2006; Ellis, 2007; Horwich
et al., 2007). Chaperones also play a key role during stresses such as heat shock, which can lead to the partial unfolding of proteins. One group of chaperones, the chaperonins (Hemmingsen et al., 1988), is typified by the Escherichia coli GroEL protein, which is the only essential chaperone in that mafosfamide organism (Fayet et al., 1989). Chaperonins are tetradecamers made up of 60 kDa subunits arranged in two heptameric rings, each with a central cavity where protein folding can occur. Each subunit has three domains referred to as the apical, intermediate and equatorial domains (Braig et al., 1994). Bacterial chaperonins interact with a separate heptameric co-chaperonin. In E. coli, the co-chaperonin (GroES) is also essential (Fayet et al., 1989). Generically, chaperonins are referred to as Cpn60 proteins, and the co-chaperonins as Cpn10 proteins (Coates et al., 1993). Chaperonins bind their client proteins by hydrophobic interactions, initially to the apical domain (Fenton et al., 1994). Binding of the co-chaperonin displaces the bound protein into the cavity, where it can fold without interacting with other proteins with which it might aggregate. The cycle of binding and release of co-chaperonin and client protein is mediated by ATP binding and hydrolysis, via a complex set of allosteric interactions within and between the two rings (reviewed in Saibil et al., 2001; Horwich et al., 2007).