The Initiation Codon Affects Ribosome Binding and Translational Efficiency in Escherichia coli of c I mRNA with or without the 5′ Untranslated Leader

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Abstract
Translational efficiency of an AUG, CUG, GUG, or UUG initiation codon was measured for the naturally leaderless c I mRNA from bacteriophage λ. In a c I- lacZ translational fusion, only AUG supported a high level of expression; GUG supported a low level of expression, while UUG and CUG expression was barely above background levels. Addition of an untranslated lac leader and Shine-Dalgarno sequence to c I increased expression but still showed a dependence on an AUG for maximum expression. c I- lacZ mRNA with an AUG initiation codon showed a greater in vitro ribosome binding strength and a higher level of full-length in vivo mRNA, suggesting that the initiation codon is an important determinant of ribosome binding strength and translational efficiency for mRNA with or without the 5′ untranslated leader.