Formylation of initiator tRNA methionine in procaryotic protein synthesis: in vivo polarity in lactose operon expression

Abstract

Eucaryotic and procaryotic organisms differ in two aspects of their translation machinery: polycistronic messengers are expressed as a sequence of individual proteins only in procaryotes, and the initiation of protein synthesis proceeds with an initiator tRNA which is found to be modified (formylated) in procaryotes and not in eucaryotes. In the present study, we show that formylation is required in vivo for the coordinate expression of the Escherichia coli lactose operon. Our experiments are consistent with a translation mechanism using dissociated ribosomes at the 5' end of the mRNA in a reaction that is only weakly dependent on enzyme of the lactose operon of Escherichia 453 on July 8, 2020 by guest

Translational reinitiation in the presence and absence of a Shine and Dalgarno sequence

“…Restarts would not be scrutinized since a free 30S ribosome * IF3 complex is not necessarily an intermediate in the restart pathway. In fact, there is some evidence that ribosomes cross the boundary between translationally coupled cistrons as 70S particles (32) and IF3 has no affinity for 70S ribosomes.…”

One‐carbon metabolism, folate, zinc and translation

“…In translation, early experiments suggested that the formyl tag of initiator methionine was used as an allosteric effector that allowed 70S ribosomes to be reset to an initiator state, without prior dissociation into a 30S + 50S pair (Petersen et al, 1976a, b). This was expected to modulate the relative expression of genes in polycistronic operons, thus coupling the 1‐C metabolism with polarity of gene expression, a subtle way to adapt gene expression dosage to metabolism (Petersen et al , 1978). This role was not further explored for a long time, until, four decades later, Yamamoto and co‐workers established that 70S‐mediated initiation was indeed a frequent mode of translation initiation in bacteria (Yamamoto et al , 2016).…”

Poliovirus genome RNA hybridizes specifically to higher eukaryotic rRNAs

“…The foregoing suggests that if internal initiation does occur in poliovirus, albeit less frequently than external 5' end initiation, the mechanism may be quite different and perhaps utilize features of 28S rRNA not involved in 5' end initiations. It has also been proposed from studies with prokaryotes, which differ from eukaryotes in that a large fraction of translation initiation occur internally, that the 70S ribosome complex is responsible for recognition of internal initiation sites as opposed to the 30S complex which binds to the external (5' end) site (42).…”