Spiegelman G, Van Hoy B, Perego M, Day J, Trach K, Hoch J A
Department of Molecular and Experimental Medicine, Scripps Clinic and Research Foundation, La Jolla, California 92037.
J Bacteriol. 1990 Sep;172(9):5011-9. doi: 10.1128/jb.172.9.5011-5019.1990.
Secondary site mutations that restore sporulation to sporulation-defective spo0F or spo0B deletion mutants were found to reside in the spo0A gene. Sequence analysis of 23 such sof mutants showed that the sof mutations fell into six classes of missense codon changes, primarily in the conserved amino-terminal domain of the response regulator Spo0A protein. Changes were observed in codons 12, 14, 60, 92, and 121. The residues affected were predominantly located in the potential turn regions at one end of the amino-terminal conserved domain on the same topological face as the active site aspartate residues. The ability of sof mutations to suppress deficiencies in the transmitter kinases, KinA and KinB, of two-component regulatory systems was tested. All of the sof mutations suppressed the sporulation deficiency of kinA mutants but only two classes among five tested suppressed kinB mutations. sof mutants segregated Spo- colonies at high frequency. Five of these Spo- mutants were found to result from mutations in the spo0A locus that reversed the effect of the sof mutatation. One of these was sequenced and found to have the original sof mutation and a new mutation, sos, at codon 105. The accumulation of sos mutations in sof strains suggested that the sof mutations have a subtle, yet deleterious, effect on the growth of the cell. The results suggested that the sof mutations increase the avidity for or reactivity with transmitter kinases in an allele-specific manner, although in some cases it is possible that the sof mutations obviate the need for phosphorylation to activate the Spo0A protein. An alternative hypothesis is presented in which the sof mutations play the role of bypass mutations for kinases.
研究发现，能使孢子形成缺陷型spo0F或spo0B缺失突变体恢复孢子形成的二级位点突变位于spo0A基因中。对23个此类sof突变体进行序列分析表明，sof突变可分为六类错义密码子变化，主要发生在应答调节因子Spo0A蛋白保守的氨基末端结构域。在密码子12、14、60、92和121处观察到了变化。受影响的残基主要位于氨基末端保守结构域一端的潜在转角区域，与活性位点天冬氨酸残基位于同一拓扑面上。测试了sof突变抑制双组分调节系统中传递激酶KinA和KinB缺陷的能力。所有sof突变均抑制了kinA突变体的孢子形成缺陷，但在测试的五类突变中只有两类抑制了kinB突变。sof突变体高频分离出Spo-菌落。发现其中五个Spo-突变体是由spo0A基因座中的突变引起的，这些突变逆转了sof突变的作用。对其中一个进行测序，发现其具有原始的sof突变以及密码子105处的新突变sos。sos突变在sof菌株中的积累表明，sof突变对细胞生长具有微妙但有害的影响。结果表明，sof突变以等位基因特异性方式增加了对传递激酶的亲和力或反应性，尽管在某些情况下，sof突变可能消除了磷酸化激活Spo0A蛋白的必要性。本文提出了另一种假说，即sof突变起到激酶旁路突变的作用。
