Carrasco C D, Buettner J A, Golden J W
Department of Biology, Texas A&M University, College Station 77843-3258.
Proc Natl Acad Sci U S A. 1995 Jan 31;92(3):791-5. doi: 10.1073/pnas.92.3.791.
Programmed DNA rearrangements that occur during cellular differentiation are uncommon and have been described in only two prokaryotic organisms. Here, we identify the developmentally regulated rearrangement of a hydrogenase gene in heterocysts of the cyanobacterium Anabaena sp. strain PCC 7120. Heterocysts are terminally differentiated cells specialized for nitrogen fixation. Late during heterocyst differentiation, a 10.5-kb DNA element is excised from within the hupL gene by site-specific recombination between 16-bp direct repeats that flank the element. The predicted HupL polypeptide is homologous to the large subunit of [NiFe] uptake hydrogenases. hupL is expressed similarly to the nitrogen-fixation genes; hupL message was detected only during the late stages of heterocyst development. An open reading frame, named xisC, identified near one end of the hupL DNA element is presumed to encode the element's site-specific recombinase. The predicted XisC polypeptide is homologous with the Anabaena sp. strain PCC 7120 site-specific recombinase XisA. Neither XisC nor XisA shows sequence similarity to other proteins, suggesting that they represent a different class of site-specific recombinase.
在细胞分化过程中发生的程序性DNA重排并不常见，仅在两种原核生物中被描述过。在此，我们鉴定了蓝藻鱼腥藻7120异形胞中氢化酶基因的发育调控重排。异形胞是专门用于固氮的终末分化细胞。在异形胞分化后期，一个10.5 kb的DNA元件通过位于该元件两侧的16 bp直接重复序列之间的位点特异性重组从hupL基因内部被切除。预测的HupL多肽与[NiFe]摄取氢化酶的大亚基同源。hupL的表达与固氮基因相似；仅在异形胞发育后期检测到hupL信息。在hupL DNA元件一端附近鉴定出的一个开放阅读框，命名为xisC，推测其编码该元件的位点特异性重组酶。预测的XisC多肽与鱼腥藻7120位点特异性重组酶XisA同源。XisC和XisA与其他蛋白质均无序列相似性，表明它们代表了一类不同的位点特异性重组酶。
