Golden J W, Mulligan M E, Haselkorn R
Nature. 1987;327(6122):526-9. doi: 10.1038/327526a0.
In the absence of a combined nitrogen source, such as ammonia, approximately every tenth vegetative cell along filaments of the cyanobacterium Anabaena develops into a heterocyst, a terminally differentiated cell that is morphologically and biochemically specialized for nitrogen fixation. At least two specific DNA rearrangements involving the nitrogen-fixation (nif) genes occur during heterocyst differentiation, one within the nifD gene and the other near the nifS gene. The two rearrangements have several properties in common. Both occur quantitatively in all heterocyst genomes, both occur at approximately the same developmental time, late in the process of heterocyst differentiation, and both result from site-specific recombination between short repeated DNA sequences. We report here the nucleotide sequences found at the site of recombination near the nifS gene. These sequences differ from those found previously for the nifD rearrangement, suggesting that the two rearrangements are catalysed by different enzymes and may be regulated independently. We also show that the nifS gene is transcribed only from rearranged genomes.
在缺乏诸如氨等化合态氮源的情况下，沿着蓝藻鱼腥藻的丝状体，大约每十个营养细胞就会发育成一个异形胞，这是一种终末分化细胞，在形态和生化方面专门用于固氮。在异形胞分化过程中至少发生了两种涉及固氮（nif）基因的特异性DNA重排，一种发生在nifD基因内，另一种发生在nifS基因附近。这两种重排有几个共同特性。两者都在所有异形胞基因组中定量发生，都在大约相同的发育时间发生，即在异形胞分化过程的后期，并且两者都是由短重复DNA序列之间的位点特异性重组导致的。我们在此报告在nifS基因附近重组位点发现的核苷酸序列。这些序列与先前在nifD重排中发现的序列不同，这表明这两种重排是由不同的酶催化的，并且可能是独立调控的。我们还表明，nifS基因仅从重排的基因组中转录。
