Yucel I, Keen N T
Department of Plant Pathology, University of California, Riverside 92521.
Mol Plant Microbe Interact. 1994 Jan-Feb;7(1):140-7. doi: 10.1094/mpmi-7-0140.
Certain Pseudomonas syringae pathovars harbor avrD alleles belonging to two different homology classes. The nonfunctional avrD allele of P. s. pv. glycinea is highly homologous to active class II avrD alleles but has five unique amino acid substitutions. Three of these five amino acid changes were shown to be absolutely required for restoration of avrD activity to the P. s. pv. glycinea allele by oligonucleotide site-directed mutagenesis. They were cysteine 19 to arginine, alanine 280 to valine, and leucine 304 to serine. In addition, changing leucine 301 to phenylalanine was required for high activity. However, alteration of the leucine at position 245 of the P. s. pv. glycinea allele to serine, present in the active alleles, did not affect avrD activity. Results from recombinant gene constructs between the nonfunctional P. s. pv. glycinea avrD gene and the functional allele from P. s. pv. phaseolicola identified six other amino acid residues that may form contextual motifs important for AvrD function. These were a four amino acid stretch comprised of glutamate 41, alanine 42, asparagine 43 and arginine 44 in addition to aspartate 243 and phenylalanine 301. Some divergence is tolerated within the four amino acid motif, but phenylalanine 301 appears to be necessary for highly active class II avrD proteins.
某些丁香假单胞菌致病型含有属于两个不同同源类别的avrD等位基因。大豆疫霉的无功能avrD等位基因与活性II类avrD等位基因高度同源，但有五个独特的氨基酸替换。通过寡核苷酸定点诱变表明，这五个氨基酸变化中的三个对于将avrD活性恢复到大豆疫霉等位基因是绝对必需的。它们分别是半胱氨酸19变为精氨酸、丙氨酸280变为缬氨酸以及亮氨酸304变为丝氨酸。此外，将亮氨酸301变为苯丙氨酸是获得高活性所必需的。然而，将大豆疫霉等位基因第245位的亮氨酸改变为活性等位基因中存在的丝氨酸，并不影响avrD活性。无功能的大豆疫霉avrD基因与菜豆疫霉功能等位基因之间的重组基因构建体的结果确定了其他六个氨基酸残基，它们可能形成对AvrD功能重要的上下文基序。这些残基除了天冬氨酸243和苯丙氨酸301外，还包括由谷氨酸41、丙氨酸42、天冬酰胺43和精氨酸44组成的四个氨基酸片段。在四个氨基酸基序内可以容忍一些差异，但苯丙氨酸301似乎是高活性II类avrD蛋白所必需的。
