Like several other bacteriophages, transposable phage Mu does not develop normally in hosts (M. which is usually constitutively expressed and is usually induced after heat shock. A 14-mer of the 57-kDa GroEL protomer associates with a 7-mer of the 10-kDa GroES protomer to form oligomers which act cooperatively in the folding of polypeptides. GroEL binds tightly to nonnative polypeptides. Upon association with GroES, by a mechanism involving ATP hydrolysis, GroEL discharges the polypeptide in a biologically active conformation (for reviews, see references 6, 17, 18, 29, and 42). The first mutants were identified by their inability to grow bacteriophage or T4. Later, GroEL and GroES were demonstrated to also participate 905579-51-3 in the lytic cycle of many other bacteriophages. In all cases, the block caused by mutations is usually in morphogenesis. However, the actions affected differ from phage to phage. For and T4, the block is usually in head assembly (for reviews, see references 2 and 9), while for T5 and 186, tail assembly is the process requiring GroELS (21, 45). Several head proteins, including gpB, are cleaved during head morphogenesis. The defective particles which accumulate in or strains contain only unprocessed head proteins (19, 20, 22, 37). GroELS was shown to be necessary for the formation of the preconnector. This small 25S complex is the first detectable intermediate in head assembly (34). It consists of 12 subunits of protein gpB, is the precursor of the head-tail connector, and serves as the initiator for the assembly of the shell (26, 27, 35). Like many other phages, Mu does not grow on 905579-51-3 some and bacteria, although replication, transcription, and lysis occur normally in such hosts. This obtaining suggests that GroELS may also be involved in Mu morphogenesis (36). The assembly of Mu virions is usually under the control of 20 genes arranged in two clusters. The first contains the head genes (13, 14). gpT is the major coat protein. It forms the head shell (16, 38). gpD and gpE are suspected of being the Rabbit polyclonal to AML1.Core binding factor (CBF) is a heterodimeric transcription factor that binds to the core element of many enhancers and promoters. Mu maturase components (5a). The protein encoded by gene exists in two forms. One, gpH, has a molecular weight which corresponds to the size predicted from the nucleotide sequence of the gene. It really is within a 25S complicated which seems to be required for a very early step in head assembly. The second, gpH*, is found in heads and is derived from gpH by proteolytic cleavage of its C-terminal end. gpH processing occurs in assembled heads before DNA packaging (14). We have analyzed Mu morphogenesis in and hosts. Our results indicate that both head and tail assembly are affected. We have traced the main block in head morphogenesis to a defect in the assembly of the 25S complex and gpH processing. MATERIALS AND METHODS Media and general procedures. Bacteria were grown in LB and titrated on LA plates containing 1.2% Difco agar (33). Phage lysates were diluted in SM buffer (40) and titrated on lawns of sensitive bacteria (0.1 ml of an overnight culture in LB) poured with 2.5 ml of 0.7% LA agar on LA plates. The phages and bacterial strains used are outlined in Table ?Table1.1. The purified GroEL and GroES proteins were gifts from O. Fayet. TABLE 1 Bacteriophages and bacterial strains?used (Sup0)11?C600and hosts. Mu growth was tested on several and hosts, among which some did and some did not allow the phage to form plaques 905579-51-3 (36a). Among the latter, two strains (and strain (lysogens was severely reduced, the number of plaque-forming phages varying from.