[mRNA with an extended Shine-Dalgarno sequence is translated independently of ribosomal protein S1].

The role of the ribosomal protein S1 in translation of a mRNA containing an extended Shine-Dalgarno sequence has been investigated. Using the toe printing technique, the formation of a ternary initiation complex with both S1-depleted 30S subunits and subunits treated with anti-S1 antibodies and mini-mRNA containing an lambda-cro-mRNA translational initiation region with a very long (9 nucleotides) Shine-Dalgarno sequence, has been demonstrated. It is concluded that initiation of translation on mRNA with extended SD-sequence is S1-independent. By means of an E. coli cell-free system of translation (S-100 extract), the translation of mini-cro-mRNA by S1-depleted ribosomes has been shown. In contrast with mini-cro-mRNA, the 30S subunits without protein S1 are inactive both in the ternary initiation complex formation and in cell-free translation with MS2 or fr phage RNAs and RNA protein III of phage fd.