Investigation of 5' messenger RNA stability determinants in lacZ

A series of initiation codon and Shine-Dalgarno (SD) sequence changes shows that the SD but not the initiation codon is necessary to maintain lacZ mRNA stability in Escherichia coli. A point mutation in the 4th codon (transcript base 55) of lacZ decreases mRNA stability and beta-galactosidase activity. This mutation also causes decreased beta-galactosidase activity in the background of altered SD and initiation codons. However, mRNA stability is not decreased in the presence of base 55-C and altered initiation codons. Downstream lacZ sequence up to codon 62 is also important for base 55-C's effect on gene expression. Therefore, ribosomal binding but not translation of the coding region is thought to be required for lacZ mRNA stability.