番茄红素β-环化酶（LYC-B）催化番茄红素形成β-胡萝卜素，是β-胡萝卜素生物合成的关键酶之一。从甘薯块根总RNA逆转录的cDNA中扩增出lyc-b的保守序列后，用cDNA末端快速扩增方法（RACE）获得了该基因全长cDNA，共1 844 bp，开放阅读框1 503 bp，编码501个氨基酸。构建了lyc-b植物表达载体p23-lyc-b，通过农杆菌介导法转化烟草，经PCR及Southern杂交表明该基因已整合到烟草的基因组中。
Lycopene β-cyclase, which catalyzes linear lycopene to cycle and become β-carotene, is one of key enzymes in the β-carotene biosynthesis pathway. Total RNA was purified from sweetpotato tuberous roots and was reverse-transcripted into cDNA, and the consensus sequence of the gene for lycopene β-cyclase (lyc-b) was amplified from the cDNA, then total cDNA sequence of lyc-b was obtained by the ways of Rapid Amplification of cDNA End (RACE). Sequence analysis showed that the complete sequence of lyc-b consists of 1 844 bp, which has an Open Reading Frame of 1 503 bp and encodes a protein of 501 amino acids. The gene was constructed into plant express vector p23-lyc-b，and was transferred into tobacco by Agrobacterium-mediated method. The results of PCR and Southern blot showed that the gene was integrated into tobacco genome.
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