Ulmasov T, Larkin R M, Guilfoyle T J
Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA.
J Biol Chem. 1996 Mar 1;271(9):5085-94. doi: 10.1074/jbc.271.9.5085.
Two subunits in RNA polymerase II (e.g. RPB3 and RPB11 in yeast) and two subunits common to RNA polymerases I and III (e.g. AC40 and AC19 in yeast) contain one or two motifs related to the alpha subunit in prokaryotic RNA polymerases. We have sequenced two different cDNAs (AtRPB36a and AtRPB36b), the two corresponding genes from Arabidopsis thaliana that are homologs of yeast RPB3, and an Arabidopsis cDNA (AtRPB13.6) that is a homolog of yeast RPB11. The B36a subunit is the predominant B36 subunit associated with RNA polymerase II purified from Arabidopsis suspension culture cells, and this subunit has a stoichiometry of about 1. Results from protein association assays showed that the B36a and B36b subunits did not associate, but each of these subunits did associate with the B13.6 subunit in vivo and in vitro. Two motifs in the B36b subunit related to the prokaryotic alpha subunit were shown to be required for the in vitro interactions with the B13.6 subunit. Our results suggest that the B36 and B13.6 subunits associate to form heterodimers in Arabidopsis RNA polymerase II like the AC40 and AC19 heterodimers reported for yeast RNA polymerases I and III but unlike the B44 homodimers reported for yeast RNA polymerase II.
RNA聚合酶II中的两个亚基（如酵母中的RPB3和RPB11）以及RNA聚合酶I和III共有的两个亚基（如酵母中的AC40和AC19）含有一个或两个与原核RNA聚合酶中的α亚基相关的基序。我们对来自拟南芥的两个不同的cDNA（AtRPB36a和AtRPB36b）、酵母RPB3的两个同源对应基因以及酵母RPB11的同源拟南芥cDNA（AtRPB13.6）进行了测序。B36a亚基是与从拟南芥悬浮培养细胞中纯化的RNA聚合酶II相关的主要B36亚基，且该亚基的化学计量比约为1。蛋白质结合试验结果表明，B36a和B36b亚基不结合，但这些亚基中的每一个在体内和体外均与B13.6亚基结合。B36b亚基中与原核α亚基相关的两个基序被证明是其与B13.6亚基进行体外相互作用所必需的。我们的结果表明，B36和B13.6亚基在拟南芥RNA聚合酶II中结合形成异二聚体，类似于酵母RNA聚合酶I和III中报道的AC40和AC19异二聚体，但与酵母RNA聚合酶II中报道的B44同二聚体不同。
