tailieunhanh - Báo cáo khoa học: Suppression of a cold-sensitive mutant initiation factor 1 by alterations in the 23S rRNA maturation region

Genetic selection has been used to isolate second-site suppressors of a defective cold-sensitive initiation factor I (IF1) R69L mutant ofEscherichia coli. The suppressor mutants specifically map to a single rRNA operon on a plasmid in a strain with all chromosomal rRNA operons deleted. | 1FEBS Journal Suppression of a cold-sensitive mutant initiation factor 1 by alterations in the 23S rRNA maturation region Jaroslav M. Belotserkovsky Georgina I. Isak and Leif A. Isaksson Department of Genetics Microbiology and Toxicology Stockholm University Sweden Keywords Escherichia coli RNase III rRNA mutation rRNA processing translation Correspondence L. A. Isaksson Department of Genetics Microbiology and Toxicology Stockholm University S-10691 Stockholm Sweden Fax 46 8 164315 Tel 46 8 164197 E-mail Received 24 January 2011 revised 1 March 2011 accepted 14 March 2011 Genetic selection has been used to isolate second-site suppressors of a defective cold-sensitive initiation factor I IF1 R69L mutant of Escherichia coli. The suppressor mutants specifically map to a single rRNA operon on a plasmid in a strain with all chromosomal rRNA operons deleted. Here we describe a set of suppressor mutations that are located in the processing stem of precursor 23S rRNA. These mutations interfere with processing of the 23S rRNA termini. A lesion of RNase III also suppresses the cold sensitivity. Our results suggest that the mutant IF1 strain is perturbed at the level of ribosomal subunit association and the suppressor mutations partially compensate for this defect by disrupting rRNA maturation. These results support the notion that IF1 is an RNA chaperone and that translation initiation is coupled to ribosomal maturation. doi Introduction Bacterial protein synthesis as directed by the action of the ribosome can be broadly divided into four main phases - initiation elongation termination and recycling. Initiation is the rate-limiting step 1 . This phase is mediated by initiation factor 1 IF1 initiation factor 2 and initiation factor 3. IF1 is the smallest of the initiation factors 2 . Its structure has been determined by NMR spectroscopy revealing that IF1 is a member of the oligomer-binding OB-fold family of proteins .