Affiliation:
1. Department of Biochemistry & Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA
2. Department of Microbiology and Molecular Medicine, University of Geneva, Geneva, Switzerland
Abstract
ABSTRACT
Bacterial ribosomes frequently translate to the 3′ end of an mRNA without terminating at a stop codon. Almost all bacteria use the transfer-messenger RNA (tmRNA)-based
trans
-translation pathway to release these “nonstop” ribosomes and maintain protein synthesis capacity.
trans
-translation is essential in some species, but in others, such as
Caulobacter crescentus
,
trans
-translation can be inactivated. To determine why
trans
-translation is dispensable in
C. crescentus
, a Tn-seq screen was used to identify genes that specifically alter growth in cells lacking
ssrA
, the gene encoding tmRNA. One of these genes,
CC1214
, was essential in Δ
ssrA
cells. Purified CC1214 protein could release nonstop ribosomes
in vitro
. CC1214 is a homolog of the
Escherichia coli
ArfB protein, and using the CC1214 sequence, ArfB homologs were identified in the majority of bacterial phyla. Most species in which
ssrA
has been deleted contain an ArfB homolog, suggesting that release of nonstop ribosomes may be essential in most or all bacteria.
IMPORTANCE
Genes that are conserved across large phylogenetic distances are expected to confer a selective advantage. The genes required for
trans
-translation,
ssrA
and
smpB
, have been found in >99% of sequenced bacterial genomes, suggesting that they are broadly important. However, these genes can be deleted in some species without loss of viability. The identification and characterization of
C. crescentus
ArfB reveals why
trans
-translation is not essential in
C. crescentus
and suggests that many other bacteria are likely to use ArfB to survive when
trans
-translation is compromised.
Publisher
American Society for Microbiology