The full-length cDNA sequence of ribulose-1，5-bisphosphate carboxylase/oxygenase small subunit
（BcrbcS）gene was cloned from the leaves of pakchoi cultivar‘Suzhouqing’with resistance to downy mildew by
RACE technique．This paper analyzed the expression pattern of this gene under different tissues by qRT-PCR and
also prokaryotic expression characteristics of this gene by SDS-PAGE technology．Results of sequence analysis
showed that the full-length cDNA of BcrbcS gene was 733 bp，among which the length of open reading frame
was 543 bp．The total encodings were 181 amino acids．The molecular mass was 20.3×10³ Da，and theoretical
isoelectric point was 8.23．The phylogenetic analysis of amino acid homology showed that the pakchoi BcrbcS gene
had similar evolutionary relationship with the other plants in the same family．Results of quantitative real-time
analysis showed that the expression of BcrbcS gene was the strongest in pakchoi leaves．The expression of BcrbcS
gene in pakchoi peaked at 24 hours after infection with SA and NaCl．Prokaryotic expression vector was induced by
IPTG to express a fusion protein with a molecular weight of about 20×10³ Da．