Hajnsdorf E, Carpousis A J, Régnier P
CNRS URA1139, Institut de Biologie Physico-chimique, Paris, France.
J Mol Biol. 1994 Jun 17;239(4):439-54. doi: 10.1006/jmbi.1994.1387.
The two cleavages made by RNase III in the transcripts of the pnp gene of Escherichia coli, 80 nucleotides upstream of the coding sequence of polynucleotide phosphorylase, were previously demonstrated to trigger the rapid degradation of the pnp messenger. In this paper, we demonstrate that the 5' end of the RNase III processed pnp mRNA is attacked by ribonucleases more efficiently than the rest of the molecule. Several 5' extremities resulting from cleavages occurring in the first 500 nucleotides of the pnp transcript have been identified. Three of them referred to as X, Y and W occur in the wild-type strain at the beginning of the coding sequence of the pnp mRNA. The mRNA appears to be cleaved more efficiently at the X site, proximal to the initiation codon, than at sites Y and W located downstream. In vitro, the maturation at X is catalysed by RNase E but not by RNase III. Accumulation of RNA processed at X in RNase E deficient strains leads us to postulate that X is a high affinity primary site which is slowly cleaved by the residual activity of thermosensitive RNase E at non-permissive temperature and that secondary sites located downstream are processed less efficiently than X. Taken together, our results suggest that in wild-type E. coli the degradation of the RNase III processed mRNA is mediated by RNase E.
核糖核酸酶III在大肠杆菌多核苷酸磷酸化酶编码序列上游80个核苷酸处对pnp基因转录本进行的两次切割，先前已证明会引发pnp信使RNA的快速降解。在本文中，我们证明核糖核酸酶III加工后的pnp信使RNA的5'端比分子的其余部分更容易受到核糖核酸酶的攻击。已鉴定出pnp转录本前500个核苷酸中切割产生的几个5'末端。其中三个分别称为X、Y和W，在野生型菌株中出现在pnp信使RNA编码序列的起始处。信使RNA在靠近起始密码子的X位点似乎比位于下游的Y和W位点切割得更有效。在体外，X位点的成熟由核糖核酸酶E催化，而不是由核糖核酸酶III催化。在核糖核酸酶E缺陷菌株中，在X位点加工的RNA积累使我们推测X是一个高亲和力的主要位点，在非允许温度下，它会被热敏核糖核酸酶E的残余活性缓慢切割，并且位于下游的次要位点的加工效率低于X。综上所述，我们的结果表明，在野生型大肠杆菌中，核糖核酸酶III加工后的信使RNA的降解是由核糖核酸酶E介导的。
