中文摘要：

鱼腥藻PCC 7120是研究细胞分化和图式形成的最简单的模式生物，因为其仅由一列原核细胞组成，在缺氮诱导条件下分化出异形胞，大致形成每间隔10个左右营养细胞（光合）出现一个异形胞（固氮）的图式．在异形胞分化机理的研究中，主调控因子如何控制异形胞形成基因和图式形成基因是关键所在．本研究的目的即是分析主调控因子HetR对一个图式形成基因patA以的调控机理以及对其他基因的调控模式．通过体外实验证明，HetR确实能够结合我们以前预测的patA上游的识别位点：将该位点缺失掉导致patA不能在营养细胞表达，而其在异形胞的表达则依赖于男一调控因子．pn聃突变株只能在长藻丝两端形成异形胞，通过导入带有上游序列的完整的patA进行互补可恢复有规律间隔形成异形胞的表型，但缺失HetR识别位点则不能互补．通常认为主调控因子在异形胞或原异形胞中上调表达，受其调控的基因也在这些分化细胞上调表达并参与异形胞形成过程．本研究则发现，HetR通过激活patA在营养细胞的表达影响正常图式的形成．此外，本研究证明，HetR还可以抑制某些基因在异形胞或全藻丝的表达，共有4种不同调控模式．

英文摘要：

Upon nitrogen step-down, Anabaena sp. PCC 7120 produces semi-regularly spaced heterocysts along filaments. HetR, the master regulator of heterocyst differenti- ation, has been shown to up-regulate hetP and hetZ in differentiating heterocysts via specific recognition sites. HetR is also predicted to bind to the promoter of patA, a gene required for heterocyst formation at intercalary positions. Here, we show that HetR binds to the predicted site 5′ from patA. Moreover, （1） deletion of the HetR-binding site greatly diminished the expression ofpatA in vegetative cells as shown with gfp, and （2） complementation of a patA mutant by a replicating plasmid that bears patA is largely prevented by removal of that binding site. In contrast, HetR- binding sites suppressed the expression of alr0202 （a homolog of hetZ） specifically in heterocysts and of alr3234 （a homolog of hetP） in whole filaments. Our results indicate that HetR can regulate gene expression in different modes.