Mechanism of regulating the expression of λN gene by ribosomal protein at translational level

In ribosomal protein S12 mutant or L24 mutant the expression of λΝ gene was depressed at translational level. To study its mechanism the λΝ gene region of λΝ lacZ gene fusion was trimmed from its 5′ end to 3′ end with DNA exonuclease III (DNA exoIII) in order to alter the TIR (translational initiation region) and the coding region of λΝ gene. After DNA sequencing 23 species of different λΝ lacZ fused genes were obtained. The β galactosidase activities of these deletants in ribosomal protein mutant were compared with that in wild type strain. The result indicated that (i) S12 mutant could affect 30S subunit’s binding to the TIR of λΝ gene messenger and cause the difficulty in forming 30S initiation complex and then decrease the efficiency of translational initiation; (ii) in S12 mutant the coding region of λΝ gene also affected the expression of λΝ gene; (iii) in L24 mutant the inhibition of λΝ gene expression was not related to translational initiation and the 5′ end of the coding region of λN gene, but related to the 3′ end of λΝ gene.