Riazanova A Iu, Molochkov N V, Abrosimova L A, Alekseevskiĭ A V, Kariagina A S, Protsenko A S, Friedhoff P, Oretskaia T S, Kubareva E A
Mol Biol (Mosk). 2010 Sep-Oct;44(5):911-21.
(Cytosine-5)-DNA methyltransferase SsoII (M.SsoII) has a long N-terminal region (1-71 residues) preceding the sequence with conservative motifs, which are characteristic for all DNA methyltransferases of such kind. The presence of this region provides M.SsoII capability to act as a transcription regulator in SsoII restriction-modification system. To perform its regulatory function, M.SsoII binds specifically to a 15-mer inverted repeat in the promoter region of SsoII restriction-modification system genes. In the present work, properties of the protein delta(72-379)M.Ecl18kI are studied, which is a deletion mutant of the SsoII-like DNA-methyltransferase M.Ecl18kI and is homologous to M.SsoII N-terminal region. delta(72-379)M.Ecl18kI capability to bind specifically a DNA duplex containing the regulatory site is demonstrated. However, such a binding takes place only in the presence of high protein excess relative to DNA, which could indicate an altered structure in the deletion mutant in comparison with the full-length M.SsoII. Circular dichroism spectroscopy demonstrated that delta(72-379)M.Ecl18kI has a strongly pronounced secondary structure and contains 32% a-helices and 20% beta-sheets. Amino acid sequences alignment of M.SsoII N-terminal region and transcription factors of known spatial structure is made. An assumption is made how alpha-helices and beta-sheets are arranged in M.SsoII N-terminal region.
（胞嘧啶-5）-DNA甲基转移酶SsoII（M.SsoII）在具有保守基序的序列之前有一个较长的N端区域（1-71个残基），这些保守基序是此类所有DNA甲基转移酶的特征。该区域的存在赋予M.SsoII在SsoII限制修饰系统中作为转录调节因子的能力。为了执行其调节功能，M.SsoII特异性结合SsoII限制修饰系统基因启动子区域中的一个15聚体反向重复序列。在本研究中，对蛋白质delta(72-379)M.Ecl18kI的特性进行了研究，它是SsoII样DNA甲基转移酶M.Ecl18kI的缺失突变体，与M.SsoII的N端区域同源。证明了delta(72-379)M.Ecl18kI特异性结合含有调节位点的DNA双链体的能力。然而，这种结合仅在相对于DNA存在高蛋白过量的情况下发生，这可能表明与全长M.SsoII相比，缺失突变体的结构发生了改变。圆二色光谱表明，delta(72-379)M.Ecl18kI具有强烈明显的二级结构，包含32%的α-螺旋和20%的β-折叠。对M.SsoII N端区域和已知空间结构的转录因子进行了氨基酸序列比对。对α-螺旋和β-折叠在M.SsoII N端区域中的排列方式进行了推测。
