Lahiri S D, Yao J, McCumbers C, Allison L A
Department of Biochemistry, University of Nebraska-Lincoln, Beadle Center, 68588-0664, USA.
Mol Cell Biol Res Commun. 1999 Apr;1(1):14-20. doi: 10.1006/mcbr.1999.0102.
The principal transcription machinery functioning in chloroplasts of higher plants is encoded in two subcellular compartments. Subunits of the RNA polymerase catalytic core are plastid encoded, while sigma factors required for promoter recognition are encoded in the nucleus. We have isolated nuclear-encoded cDNAs, sig1, sig2, and sig3, specifying three sigma factors from maize (Zea mays). The three deduced polypeptides have extensive sequence identity with the principal sigma factors of eubacteria. Two of the maize cDNAs, sig1 and sig3, encode NH2-terminal transit peptides which direct the uptake of a heterologous protein into chloroplasts in vitro. Transcripts for the sig3 gene were more abundant in green leaves than in roots and in light-treated seedlings than in dark-grown seedlings. In contrast, sig1 transcripts were readily detectable in all tissues examined. Thus, at least two promoter-selectivity factors function with the maize chloroplast RNA polymerase, one of which is constitutively expressed and the other is light activated.
高等植物叶绿体中起作用的主要转录机制由两个亚细胞区室编码。RNA聚合酶催化核心的亚基由质体编码，而启动子识别所需的σ因子则由细胞核编码。我们已经分离出了核编码的cDNA，即sig1、sig2和sig3，它们分别指定了来自玉米（Zea mays）的三种σ因子。这三种推导出来的多肽与真细菌的主要σ因子具有广泛的序列同一性。玉米的两个cDNA，sig1和sig3，编码NH2末端转运肽，这些肽在体外可指导异源蛋白进入叶绿体。sig3基因的转录本在绿叶中比在根中更丰富，在光照处理的幼苗中比在黑暗生长的幼苗中更丰富。相比之下，sig1转录本在所有检测的组织中都很容易检测到。因此，至少有两个启动子选择性因子与玉米叶绿体RNA聚合酶一起发挥作用，其中一个是组成型表达的，另一个是光激活的。
