Hamilton D L, Luftig R B
J Virol. 1976 Feb;17(2):550-67. doi: 10.1128/JVI.17.2.550-567.1976.
Several aspects of the terminal stages of T4 head maturation were investigated using ts and am mutants blocked at single steps of the assembly pathway. We had previously found that cells infected with mutants of gene 13, e.g., tsN38 and amE609, accumulated both stable (10 to 20%)- and fragile (80%)-filled head precursors (Hamilton and Luftig, 1972). Here we showed the following for such gene 13-defective, mutant-infected cells. (i) Using thin-section analysis the pool of phage precursor structures observed under nonpermissive conditions was one-third of that observed when the cells were cultured under permissive conditions. (ii) In order for complete conversion of the precursors into viable phage to occur, there were apparent requirements of metabolic energy, protein, and DNA synthesis. (iii) The intracellular DNA pool under nonpermissive conditions exhibited a 50% distribution between 63S (mature size) and 200 S (concatenate size) DNA, with the latter DNA serving as a precursor pool. Further, this DNA pool when spread onto a protein monolayer exhibited a dispersed array of DNA, strands around a core, which was less dense than that found for the greater than 1,000S DNA concatenate isolated from gene 49-defective infected cells. (iv) When precuations were taken to stabilize the head precursors, such as lysis of the cells into glutaraldehyde, there was a 30% increase in the yield of 1,200S filled heads. Correlating these results and previous results concerning gene 49-defective unfilled heads, we propose that there are several forms of gene 13 fragile head precursors which serve as intermediates between gene 49 unfilled heads and gene 13 stable filled heads. We cannot, however, rule out the possibility that all gene 13-defective heads represent a single class of unstable particles, which decay slowly. In either case, we have shown that gene 13-defective particles are unstable to some degree inside the cell and are highly unstable outside the cell; yet all particles can still be efficiently converted to phage in vivo.
利用在装配途径的单个步骤受阻的温度敏感型（ts）和琥珀突变型（am）突变体，对T4噬菌体头部成熟终末阶段的几个方面进行了研究。我们之前发现，用基因13的突变体（如tsN38和amE609）感染细胞时，会积累稳定填充（10%至20%）和易碎填充（80%）的头部前体（汉密尔顿和卢夫蒂格，1972年）。在此，我们展示了对于这类基因13缺陷型突变体感染细胞的以下情况。（i）使用超薄切片分析，在非允许条件下观察到的噬菌体前体结构库是细胞在允许条件下培养时观察到的结构库的三分之一。（ii）为了使前体完全转化为有活力的噬菌体，明显需要代谢能量、蛋白质和DNA合成。（iii）在非允许条件下，细胞内DNA库在63S（成熟大小）和200S（连环体大小）DNA之间呈现50%的分布，后者的DNA作为前体库。此外，当将该DNA库铺展在蛋白质单层上时，呈现出围绕核心的分散DNA链阵列，其密度低于从基因49缺陷型感染细胞中分离出的大于1000S的DNA连环体。（iv）当采取措施稳定头部前体时，例如将细胞裂解到戊二醛中，1200S填充头部的产量增加了30%。将这些结果与之前关于基因49缺陷型未填充头部的结果相关联，我们提出基因13易碎头部前体有几种形式，它们作为基因49未填充头部和基因13稳定填充头部之间的中间体。然而，我们不能排除所有基因13缺陷型头部代表一类单一的不稳定颗粒且缓慢衰变的可能性。在任何一种情况下，我们都表明基因13缺陷型颗粒在细胞内某种程度上是不稳定的，在细胞外高度不稳定；然而所有颗粒在体内仍能有效地转化为噬菌体。
