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Translation initiation factor eIF5B promotes GTP-dependent ribosomal subunit joining in the final step of the translation initiation pathway. The protein resembles a chalice with the α-helix H12 forming the stem connecting the GTP-binding domain cup to the domain IV base. Helix H12 has been proposed to function as a rigid lever arm governing domain IV movements in response to nucleotide binding and as a molecular ruler fixing the distance between domain IV and the G domain of the factor. To investigate its function, helix H12 was lengthened or shortened by one or two turns. In addition, six consecutive residues in the helix were substituted by Gly to alter the helical rigidity. Whereas the mutations had minimal impacts on the factor's binding to the ribosome and its GTP binding and hydrolysis activities, shortening the helix by six residues impaired the rate of subunit joining in vitro and both this mutation and the Gly substitution mutation lowered the yield of Met-tRNAiMetbound to 80S complexes formed in the presence of nonhydrolyzable GTP. Thus, these two mutations, which impair yeast cell growth and enhance ribosome leaky scanning in vivo, impair the rate of formation and stability of the 80S product of subunit joining. These data support the notion that helix H12 functions as a ruler connecting the GTPase center of the ribosome to the P site where Met-tRNAiMetis bound and that helix H12 rigidity is required to stabilize Met-tRNAiMetbinding.

The organisms of the genus Vibrio can cause disease in humans, with the most widely infective organism being Vibrio cholerae, which causes cholera. Eleven species of Vibrio have been isolated from clinical specimens. Some of these isolates have been shown to cause disease, while the pathogenicity of others have not yet been determined. The bacteria of the Vibrio species are found primarily in salty and brackish water, mostly in the summer and fall seasons. They are present in shellfish and various fish. Clinical symptoms of infection with Vibrio include gastroenteritis, wound infection, ear infection, and infection in the blood. A case study is presented of a new strain, Vibrio carchariae, which was transmitted to an individual by a shark and caused serious infection of the wounds caused by the shark. Damaged tissue and cellular debris had to be removed from the wound by surgery. The bacteria did not extensively invade other tissues, nor was this strain toxic to the whole body. There are only a few reports of the infection of human wounds from shark bites. However, research has shown that various bacteria, including various species of Vibrio, are present on the teeth of sharks. Therefore, treatment of infected wounds that have occurred by marine animals, including sharks, should include antibiotics such as tetracyclines, aminoglycosides, and cephalosporins, which are effective against various species of Vibrio. (Consumer Summary produced by Reliance Medical Information, Inc.)