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The downstream atpE cistron is efficiently translated via its own cis-element in partially overlapping atpB-atpE dicistronic mRNAs in chloroplasts.

ABSTRACT: The chloroplast atpB and atpE genes encode subunits ? and ? of the ATP synthase, respectively. They are co-transcribed as dicistronic mRNAs in flowering plants. An unusual feature is an overlap (AUGA) of the atpB stop codon (UGA) with the atpE start codon (AUG). Hence, atpE translation has been believed to depend on atpB translation (i.e. translational coupling). Using an in vitro translation system from tobacco chloroplasts, we showed that both atpB and atpE cistrons are translated from the tobacco dicistronic mRNA, and that the efficiency of atpB translation is higher than that of atpE translation. When the atpB 5'-UTR was replaced with lower efficiency 5'-UTRs, atpE translation was higher than atpB translation. Removal of the entire atpB 5'-UTR arrested atpB translation but atpE translation still proceeded. Introduction of a premature stop codon in the atpB cistron did not abolish atpE translation. These results indicate that atpE translation is independent of atpB translation. Mutation analysis showed that the atpE cistron possesses its own cis-element(s) for translation, located ~25?nt upstream from the start codon.

SUBMITTER: Suzuki H

PROVIDER: S-EPMC3241655 | biostudies-literature | 2011 Nov

REPOSITORIES: biostudies-literature

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The downstream atpE cistron is efficiently translated via its own cis-element in partially overlapping atpB-atpE dicistronic mRNAs in chloroplasts.

Suzuki Haruka H Kuroda Hiroshi H Yukawa Yasushi Y Sugiura Masahiro M

Nucleic acids research 20110816 21

The chloroplast atpB and atpE genes encode subunits β and ε of the ATP synthase, respectively. They are co-transcribed as dicistronic mRNAs in flowering plants. An unusual feature is an overlap (AUGA) of the atpB stop codon (UGA) with the atpE start codon (AUG). Hence, atpE translation has been believed to depend on atpB translation (i.e. translational coupling). Using an in vitro translation system from tobacco chloroplasts, we showed that both atpB and atpE cistrons are translated from the tob ...[more]

PMID: 21846772

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Project description:BackgroundThe genus Orbivirus includes several species that infect livestock - including Bluetongue virus (BTV) and African horse sickness virus (AHSV). These viruses have linear dsRNA genomes divided into ten segments, all of which have previously been assumed to be monocistronic.ResultsBioinformatic evidence is presented for a short overlapping coding sequence (CDS) in the Orbivirus genome segment 9, overlapping the VP6 cistron in the +1 reading frame. In BTV, a 77-79 codon AUG-initiated open reading frame (hereafter ORFX) is present in all 48 segment 9 sequences analysed. The pattern of base variations across the 48-sequence alignment indicates that ORFX is subject to functional constraints at the amino acid level (even when the constraints due to coding in the overlapping VP6 reading frame are taken into account; MLOGD software). In fact the translated ORFX shows greater amino acid conservation than the overlapping region of VP6. The ORFX AUG codon has a strong Kozak context in all 48 sequences. Each has only one or two upstream AUG codons, always in the VP6 reading frame, and (with a single exception) always with weak or medium Kozak context. Thus, in BTV, ORFX may be translated via leaky scanning. A long (83-169 codon) ORF is present in a corresponding location and reading frame in all other Orbivirus species analysed except Saint Croix River virus (SCRV; the most divergent). Again, the pattern of base variations across sequence alignments indicates multiple coding in the VP6 and ORFX reading frames.ConclusionAt approximately 9.5 kDa, the putative ORFX product in BTV is too small to appear on most published protein gels. Nonetheless, a review of past literature reveals a number of possible detections. We hope that presentation of this bioinformatic analysis will stimulate an attempt to experimentally verify the expression and functional role of ORFX, and hence lead to a greater understanding of the molecular biology of these important pathogens.

Dataset Information

The downstream atpE cistron is efficiently translated via its own cis-element in partially overlapping atpB-atpE dicistronic mRNAs in chloroplasts.

Publications

The downstream atpE cistron is efficiently translated via its own cis-element in partially overlapping atpB-atpE dicistronic mRNAs in chloroplasts.

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