Zwieb C
Department of Molecular Biology, University of Texas Health Science Center at Tyler 75710.
Eur J Biochem. 1994 Jun 15;222(3):885-90. doi: 10.1111/j.1432-1033.1994.tb18936.x.
The RNA component of signal recognition particle (SRP) consists of eight helices which form a functional unit with the proteins of the SRP. The primary binding site of the 19-kDa protein of SRP (SRP19) is a tetranucleotide loop (tetraloop) in helix 6 of the SRP RNA, but additional determinants are located in helix 8, which might play important roles in the assembly and the function of the particle. To determine the structural features in helix 8 essential for interaction with SRP19, we altered helix 8 systematically by site-directed mutagenesis, and determined the ability of protein SRP19 to interact with the various mutant SRP RNAs. Binding of SRP19 was affected by base changes introduced into the 5' portion (192A, 193G, 194G in the human SRP RNA), but not into the 3' portion (205 A, 206G, 207C) of the distally located conserved internal loop of helix 8. Of the three bases at positions 192-194, only a pyrimidine at position 192 impaired the association with SPR19. An important feature of the SRP19-RNA interaction were the three base pairs U195-G204, C196-G203 and G197-C202 which shape the helix-8 tetraloop. Some base-specific features in the base pairs were also recognized. The tetraloop bases of helix 8 were dispensable for the interaction with SRP19.
信号识别颗粒（SRP）的RNA组分由八个螺旋组成，这些螺旋与SRP的蛋白质形成一个功能单元。SRP的19 kDa蛋白（SRP19）的主要结合位点是SRP RNA螺旋6中的一个四核苷酸环（四环），但其他决定因素位于螺旋8中，这可能在颗粒的组装和功能中起重要作用。为了确定螺旋8中与SRP19相互作用所必需的结构特征，我们通过定点诱变系统地改变了螺旋8，并确定了蛋白质SRP19与各种突变SRP RNA相互作用的能力。SRP19的结合受到引入到螺旋8远端保守内环5'部分（人SRP RNA中的192A、193G、194G）碱基变化的影响，但不受3'部分（205A、206G、207C）碱基变化的影响。在192 - 194位的三个碱基中，只有192位的嘧啶会损害与SPR19的结合。SRP19 - RNA相互作用的一个重要特征是三个碱基对U195 - G204、C196 - G203和G197 - C202，它们构成了螺旋8四环。碱基对中的一些碱基特异性特征也被识别出来。螺旋8的四环碱基对于与SRP19的相互作用是可有可无的。
