Analysis of deletion mutations of the rpsL gene in the yeast Saccharomycescerevisiae detected after long-term flight on the Russian space station Mir

Using the yeast Saccharomyces cerevisiae on board the Russian space station Mir, we studied the effects of long-term space flight on mutation of the b acterial ribosomal protein L gene (rpsL) cloned in a yeast-Escherichia coli shuttle vector. The mutation frequencies of the cloned rpsL gene on the Mi r and the ground (control) yeast samples were estimated by transformation o f E. coli with the plasmid DNAs recovered from yeast and by assessment of t he conversion of the rpsL wild-type phenotype (Sm-S) to its mutant phenotyp e (Sm-R). After a 40-day space flight, some part of space samples gave muta tion frequencies two to three times higher than those of the ground samples . Nucleotide sequence analysis showed no apparent difference in point mutat ion rates between the space and the ground mutant samples. However, the gre ater part of the Mir mutant samples were found to have a total or large del etion in the rpsL sequence, suggesting that space radiation containing high -linear energy transfer (LET) might have caused deletion-type mutations. (C ) 2000 Elsevier Science B.V. All rights reserved.