Copertino D W, Hall E T, Van Hook F W, Jenkins K P, Hallick R B
Department of Biochemistry, University of Arizona, Tucson 85721.
Nucleic Acids Res. 1994 Mar 25;22(6):1029-36. doi: 10.1093/nar/22.6.1029.
The 1605 bp intron 4 of the Euglena gracilis chloroplast psbC gene was characterized as a group III twintron composed of an internal 1503 nt group III intron with an open reading frame of 1374 nt (ycf13, 458 amino acids), and an external group III intron of 102 nt. Twintron excision proceeds by a sequential splicing pathway. The splicing of the internal and external group III introns occurs via lariat intermediates. Branch sites were mapped by primer extension RNA sequencing. The unpaired adenosines in domains VI of the internal and external introns are covalently linked to the 5' nucleotide of the intron via 2'-5' phosphodiester bonds. This bond is susceptible to hydrolysis by the debranching activity of the HeLa nuclear S100 fraction. The internal intron and presumptive ycf13 mRNA accumulates primarily as a linear RNA, although a lariat precursor can also be detected. The ycf13 gene encodes a maturase-like protein that may be involved in group III intron metabolism.
纤细裸藻叶绿体psbC基因的1605 bp内含子4被鉴定为III类双内含子，它由一个1503 nt的内部III类内含子和一个102 nt的外部III类内含子组成，内部内含子带有一个1374 nt的开放阅读框（ycf13，458个氨基酸）。双内含子切除通过连续剪接途径进行。内部和外部III类内含子的剪接通过套索中间体发生。通过引物延伸RNA测序对分支位点进行了定位。内部和外部内含子结构域VI中的未配对腺苷通过2'-5'磷酸二酯键与内含子的5'核苷酸共价连接。这种键易被HeLa细胞核S100组分的去分支活性水解。内部内含子和推测的ycf13 mRNA主要以线性RNA形式积累，不过也能检测到套索前体。ycf13基因编码一种可能参与III类内含子代谢的成熟酶样蛋白。
