Translation initiation in Drosophila melanogaster is reduced by mutations upstream of the AUG initiator codon.

Abstract

The importance to in vivo translation of sequences immediately upstream of the Drosophila alcohol dehydrogenase (Adh) start codon was examined at two developmental stages. Mutations were introduced into the Adh gene in vitro, and the mutant gene was inserted into the genome via germ line transformation. An A-to-T substitution at the -3 position did not affect relative translation rates of the ADH protein at the second-instar larval stage but resulted in a 2.4-fold drop in translation of ADH at the adult stage. A second mutant gene, containing five mutations in the region -1 to -9, was designed to completely block translation initiation. However, transformant lines bearing these mutations still exhibit detectable ADH, albeit at substantially reduced levels. The average fold reduction at the second-instar larval stage was 5.9, while at the adult stage a 12.5-fold reduction was observed.

The Role of the 5′ Untranslated Region of Eukaryotic Messenger RNAs in Translation and Its Investigation Using Antisense Technologies

“…Similar compilations of mRNA sequences derived from DrosophiZa melanogaster (33), yeast (34), and plants (35) revealed variation in the start codon context among different eukaryotic groups. The conservation of sequences around the AUG start codon suggests a functional significance with regard to translation initiation, an assumption validated by mutational studies (36)(37)(38). The conservation of sequences around the AUG start codon suggests a functional significance with regard to translation initiation, an assumption validated by mutational studies (36)(37)(38).…”

UltrabithoraxandAntennapedia5′ Untranslated Regions Promote Developmentally Regulated Internal Translation Initiation

“…Kozak (21,22) has argued that these types of mRNAs are all translated by a cap-dependent mechanism and has proposed that the upstream AUGs are ignored by the scanning preinitiation complex (leaky scanning) because they contain a poor sequence context. A thorough analysis of sequence context data by Cavener and Ray (11) and mutagenesis of translation start site context in Drosophila (12) does not support the conclusion that upstream AUGs would typically be ignored by the mechanism of leaky scanning. Consequently, it seems unlikely that mRNAs such as Antennapedia, which contain 15 upstream AUGs, could be translated via cap-dependent mechanism since traversing the long leader would require numerous rounds of termination-reinitiation, a process known to be inefficient (26).…”

Effect of two consensus sequences preceding the translation initiator codon on gene expression in plant protoplasts

“…Since the one difference between the two plasmids modifies the site of translation initiation, the most likely explanation is a difference in the efficiency of translation initiation. Translation initiation has been shown to be affected by many factors such as the length, base composition and secondary structure of the untranslated leader sequence [2,10,12]. In plants, the presence of a polylinker upstream from the translation start was shown to decrease gene expression [7].…”