TAILIEUCHUNG - Báo cáo khoa học: Abortive translation caused by peptidyl-tRNA drop-off at NGG codons in the early coding region of mRNA

InEscherichia colithe codons CGG, AGG, UGG or GGG (NGG codons) but not GGN or GNG (where N is non-G) are associated with low expres-sion of a reporter gene, if located at positions +2 to +5. Induction of a lacZ reporter gene with any one of the NGG codons at position +2 to +5 does not influence growth of a normal strain, but growth of a strain with a defective peptidyl-tRNA hydrolase (Pth) enzyme is inhibited. | iFEBS Journal Abortive translation caused by peptidyl-tRNA drop-off at NGG codons in the early coding region of mRNA Ernesto I. Gonzalez de Valdivia and Leif A. Isaksson Department of Genetics Microbiology and Toxicology Stockholm University Sweden Keywords abortive translation NGG codons peptidyl-tRNA drop-off Escherichia coli early elongation Correspondence L. A. Isaksson Department of Genetics Microbiology and Toxicology Stockholm University S-106 91 Stockholm Sweden Fax 46 8 15 51 39 Tel 46 8 16 41 97 E-mail Website http Received 29 June 2005 revised 17 August 2005 accepted 19 August 2005 doi In Escherichia coli the codons CGG AGG UGG or GGG NGG codons but not GGN or GNG where N is non-G are associated with low expression of a reporter gene if located at positions 2 to 5. Induction of a lacZ reporter gene with any one of the NGG codons at position 2 to 5 does not influence growth of a normal strain but growth of a strain with a defective peptidyl-tRNA hydrolase Pth enzyme is inhibited. The same codons if placed at position 7 did not give this effect. Other codons such as CGU and AGA at location 2 to 5 did not give any growth inhibition of either the wild-type or the mutant strain. The inhibitory effect on the pth mutant strain by NGG codons at location 5 was suppressed by overexpression of the Pth enzyme from a plasmid. However the overexpression of cognate tRNAs for AGG or GGG did not rescue from the growth inhibition associated with these codons early in the induced model gene. The data suggest that the NGG codons trigger pep-tidyl-tRNA drop-off if located at early coding positions in mRNA thereby strongly reducing gene expression. This does not happen if these codons are located further down in the mRNA at position 7 or later. As an early step during translation initiation in bacteria the mRNA is anchored to the 30S ribosomal subunit by base pairing between a sequence close to the end of

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