James Steven W, Banta Travis, Barra James, Ciraku Lorela, Coile Clifford, Cuda Zach, Day Ryan, Dixit Cheshil, Eastlack Steven, Giang Anh, Goode James, Guice Alexis, Huff Yulon, Humbert Sara, Kelliher Christina, Kobie Julie, Kohlbrenner Emily, Mwambutsa Faustin, Orzechowski Amanda, Shingler Kristin, Spell Casey, Anglin Sarah Lea
Biology Department, Gettysburg College, Gettysburg, Pennsylvania 17325
Biology Department, Millsaps College, Jackson, Mississippi 39210.
Genetics. 2014 Oct;198(2):617-33. doi: 10.1534/genetics.114.167445. Epub 2014 Aug 7.
Control of the eukaryotic G2/M transition by CDC2/CYCLINB is tightly regulated by protein-protein interactions, protein phosphorylations, and nuclear localization of CDC2/CYCLINB. We previously reported a screen, in Aspergillus nidulans, for extragenic suppressors of nimX2(cdc2) that resulted in the identification of the cold-sensitive snxA1 mutation. We demonstrate here that snxA1 suppresses defects in regulators of the CDK1 mitotic induction pathway, including nimX2(cdc) (2), nimE6(cyclinB), and nimT23(cdc) (25), but does not suppress G2-arresting nimA1/nimA5 mutations, the S-arresting nimE10(cyclinB) mutation, or three other G1/S phase mutations. snxA encodes the A. nidulans homolog of Saccharomyces cerevisiae Hrb1/Gbp2; nonessential shuttling messenger RNA (mRNA)-binding proteins belonging to the serine-arginine-rich (SR) and RNA recognition motif (RRM) protein family; and human heterogeneous ribonucleoprotein-M, a spliceosomal component involved in pre-mRNA processing and alternative splicing. snxA(Hrb) (1) is nonessential, its deletion phenocopies the snxA1 mutation, and its overexpression rescues snxA1 and ΔsnxA mutant phenotypes. snxA1 and a second allele isolated in this study, snxA2, are hypomorphic mutations that result from decreased transcript and protein levels, suggesting that snxA acts normally to restrain cell cycle progression. SNXA(HRB1) is predominantly nuclear, but is not retained in the nucleus during the partially closed mitosis of A. nidulans. We show that the snxA1 mutation does not suppress nimX2 by altering NIMX2(CDC2)/NIME(CYCLINB) kinase activity and that snxA1 or ΔsnxA alter localization patterns of NIME(CYCLINB) at the restrictive temperatures for snxA1 and nimX2. Together, these findings suggest a novel and previously unreported role of an SR/RRM family protein in cell cycle regulation, specifically in control of the CDK1 mitotic induction pathway.
CDC2/细胞周期蛋白B对真核生物G2/M期转换的调控受到蛋白质-蛋白质相互作用、蛋白质磷酸化以及CDC2/细胞周期蛋白B核定位的严格控制。我们之前报道了在构巢曲霉中对nimX2（cdc2）的基因外抑制子进行的筛选，结果鉴定出了冷敏感的snxA1突变。我们在此证明，snxA1可抑制CDK1有丝分裂诱导途径调节因子中的缺陷，包括nimX2（cdc）（2）、nimE6（细胞周期蛋白B）和nimT23（cdc）（25），但不能抑制导致G2期阻滞的nimA1/nimA5突变、导致S期阻滞的nimE10（细胞周期蛋白B）突变或其他三个G1/S期突变。snxA编码酿酒酵母Hrb1/Gbp2的构巢曲霉同源物；属于富含丝氨酸-精氨酸（SR）和RNA识别基序（RRM）蛋白家族的非必需穿梭信使RNA（mRNA）结合蛋白；以及人不均一核糖核蛋白-M，一种参与前体mRNA加工和可变剪接的剪接体成分。snxA（Hrb）（1）是非必需的，其缺失模拟了snxA1突变，其过表达可挽救snxA1和ΔsnxA突变体表型。snxA1和本研究中分离出的第二个等位基因snxA2是低表达突变，是转录本和蛋白质水平降低导致的，这表明snxA通常起到抑制细胞周期进程的作用。SNXA（HRB1）主要位于细胞核中，但在构巢曲霉部分封闭的有丝分裂过程中不会保留在细胞核中。我们表明，snxA1突变不会通过改变NIMX2（CDC2）/NIME（细胞周期蛋白B）激酶活性来抑制nimX2，并且snxA1或ΔsnxA会在snxA1和nimX2的限制温度下改变NIME（细胞周期蛋白B）的定位模式。总之，这些发现表明SR/RRM家族蛋白在细胞周期调控中具有一种新的、以前未报道过的作用，特别是在CDK1有丝分裂诱导途径的控制中。
