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The wild abortive cytoplasmic male sterility (CMS-WA) system, an ideal type of sporophytic CMS in indica rice, is used for the large-scale commercial production of hybrid rice. Searching for restorer genes is a good approach when phenotyping is very time-consuming and requires the determination of spikelet sterility in testcross progeny. To establish more precisely the genetical and physical maps of the Rf4 gene, high-resolution mapping of this locus was carried out using simple sequence repeat (SSR) markers and newly designed markers in a F2 population. The genetic linkage analysis indicated that five SSR markers (RM6737, RM304, RM171, RM5841 and RM228) on the long arm of chromosome 10 were linked with the Rf4 gene. Rf4 was flanked by two SSR markers RM171 and RM6737 at distances of 3.2 and 1.6 cM, respectively. Also, within the region between Rf4 gene and RM171, a newly designed primer pair, AB443, produced two sterile-specific markers, AB443-400 and AB443-500, 0.5 and 1.03 cM from the gene. The flanking markers identified give promise for their application in molecular marker-assisted selection (MAS) and they are also suitable for starting chromosome walking to clone Rf4 gene in the near future. [ABSTRACT FROM AUTHOR]

Peptidyl­tRNA dissociation from ribosomes is an energetically costly but apparently inevitable process that accompanies normal protein synthesis. The drop-off products of these events are hydrolysed by peptidyl-tRNA hydrolase. Mutant selections have been made to identify genes involved in the drop-off of peptidyl-tRNA, using a thermosensitive peptidyl­tRNA hydrolase mutant in Escherichia coli. Transposon insertions upstream of the frr gene, which encodes RF4 (ribosome release or recycling factor), restored growth to this mutant. The insertions impaired expression of the frr gene. Mutations inactivating prfC, encoding RF3 (release factor 3), displayed a similar phenotype. Conversely, production of RF4 from a plasmid increased the thermosensitivity of the peptidyl­tRNA hydrolase mutant. In vitro measurements of peptidyl­tRNA release from ribosomes paused at stop signals or sense codons confirmed that RF3 and RF4 were able to stimulate peptidyl­tRNA release from ribosomes, and showed that this action of RF4 required the presence of translocation factor EF2, known to be needed for the function of RF4 in ribosome recycling. When present together, the three factors were able to stimulate release up to 12-fold. It is suggested that RF4 may displace peptidyl­tRNA from the ribosome in a manner related to its proposed function in removing deacylated tRNA during ribosome recycling. [ABSTRACT FROM AUTHOR]