lN gene expression regulated by translation termination in ribosome L24 mutant

Besides transcription regulation, gene expression is also regulated at translation level. Although translation regulation is mainly mediated by translation initiation, an abundance of evidence shows that the termination phase of translation is also important for gene expression. The expression of lambdaN gene is down regulated at translation level in L24 mutant, however the precise mechanism still remains unknown. We report here that in an L24 mutant strain, the expression of lac-lambdaN and GST-lambdaN is decreased to 25% and 50% of that in wild type T83 strain respectively. Strikingly, the yield of GST-lambdaN fusion protein in L24 mutant can be restored to the level as in T83 wild type strain by changing the two codons upstream lambdaN stop codon. These findings imply that the stop codon and its context are involved in the translation regulation. The possible reason is that the translation termination complex containing L24 mutant ribosome may not dissociate properly in stop code region. This failure of disengagement from mRNA will slow down the process of following ribosomes, and consequently decrease the efficiency of lambdaN gene expression.