Gong L, Kaplan S
Department of Microbiology and Molecular Genetics, University of Texas at Houston-Medical School 77225, USA.
Microbiology (Reading). 1996 Aug;142 ( Pt 8):2057-69. doi: 10.1099/13500872-142-8-2057.
The puf operon of Rhodobacter sphaeroides 2.4.1 encode the beta- and alpha-polypeptides of the B875 complex, the L and M polypeptides of the reaction centre and the pufX gene product. A previous report from the authors' laboratory indicated the potential existence of a 20-codon open reading frame (orfK, now designated pufK) located immediately upstream of the pufB structural gene. It is now demonstrated that pufK is translated in vivo and that the specific levels or nature of the rare codons within pufK affect the expression of pufK. Using a series of pufK-specific mutations, both in trans as lacZ translational fusions and incorporated into the genome in single copy, evidence has been obtained that translation initiation through pufK may be essential to translation of pufB. Further, the abundance, quality and distribution of rare codons within pufK may serve to 'gate' the entry of ribosomes at pufB. The data also suggest that translation of pufB is uncoupled from that of pufA, with the latter capable of being produced in excess of the former. It is also revealed that the secondary structure at the 5' end of the large and small puf transcripts may play a role in mRNA stability and that stability of the small puf transcript is independent of translation.
球形红杆菌2.4.1的puf操纵子编码B875复合体的β和α多肽、反应中心的L和M多肽以及pufX基因产物。作者实验室之前的一份报告表明，在pufB结构基因上游紧邻位置可能存在一个20密码子的开放阅读框（orfK，现命名为pufK）。现已证明pufK在体内可被翻译，且pufK内稀有密码子的特定水平或性质会影响pufK的表达。通过一系列pufK特异性突变，无论是作为lacZ翻译融合体在反式中还是以单拷贝形式整合到基因组中，都已获得证据表明通过pufK的翻译起始可能对pufB的翻译至关重要。此外，pufK内稀有密码子的丰度、质量和分布可能起到在pufB处“控制”核糖体进入的作用。数据还表明，pufB的翻译与pufA的翻译解偶联，后者能够过量产生。还发现大小puf转录本5'端的二级结构可能在mRNA稳定性中起作用，并且小puf转录本的稳定性与翻译无关。
