LOCALIZATION OF THE NOVEL RNA BINDING PROTEIN SLA1 AND ITS ROLE IN CELL DIFFERENTIATION IN FISSION YEAST

Sla1是一种具有RNA识别基序（RRM）和La基序（La基序）的RNA结合蛋白，在La蛋白家族中高度保守。在这项研究中，我们首次在La同源物中提出证据，证明Sla1的截断形式对pombe Schizosaccharomyces有性发育的调节很重要。我们发现在cooh末端截断的Sla1 （Sla1DC）在ras1菌株和其他几种产孢缺陷菌株（如mapk -级联、sapk -级联和camp -级联组分的干扰物）中诱导异位产孢。Sla1全长位于细胞核内，而产孢诱导的Sla1DC位于细胞质内。与这一结果一致，Sla1在COOH末端有一个基本的NLS（核定位信号）基序。进一步的缺失分析表明，Sla1的产孢诱导效应只需要一小部分RRM，而不需要整个RRM或La基序。此外，Sla1DC诱导异位单倍体减数分裂，就像pat1-114或mei2-SATA突变体一样。Sla1DC在me3干扰物中诱导孢子形成，而在me2干扰物中则没有。这些结果强烈提示Sla1DC作用于me2的上游和me3的下游。

Sla1, a homolog of human La protein in fission yeast, has been known to be an RNA binding protein that has an RRM (RNA-Recognition Motif) and the La motif which are highly conserved among La protein families. In this study, we present the evidence, for the first time among the La homologs, that a truncated form of Sla1 is important for regulation of sexual development in Schizosaccharomyces pombe. We found that Sla1 truncated in the COOH-terminus (Sla1DC) induced ectopic sporulation in ras1 strain and other several sporulation deficient strains such as disruptants of the components of the MAPK-cascade, the SAPK-cascade and the cAMP-cascade. The full-length of Sla1 located in nucleus, but sporulation inducible Sla1DC located in cytoplasm. Consistent with this result, Sla1 has a basic NLS (Nuclear Localization Signal)-like motif in its COOH terminus. Further deletion analysis of Sla1 suggested that for sporulation inducible effect a small region that includes only a portion of RRM, but neither a whole RRM nor the La motif was required. In addition, Sla1DC induced ectopic haploid meiosis, like pat1-114 or mei2-SATA mutant do. Sla1DC induced sporulation in a mei3 disruptant but not in a mei2 disruptant. These results strongly suggested that Sla1DC acts at the upstream of Mei2 and at the downstream of Mei3.