Gerhard B, Warren R A
Biochemistry. 1982 Oct 26;21(22):5458-62. doi: 10.1021/bi00265a012.
Bacteriophage phi W-14 DNA contains the hypermodified pyrimidine alpha-putrescinylthymine (putThy) [Kropinski, A. M. B., Bose, R. J., & Warren, R. A. J. (1973) Biochemistry 12, 151]. The primary amino groups of the putrescinyl side chains react with trinitrobenzenesulfonate (TNBS) but at a much slower rate than the reactive lysine side chains of proteins. Both primary and secondary amino groups in the putrescinyl side chains react with acetic anhydride, but the reaction does not go to completion under the conditions employed. Some of the secondary amino groups react faster with acetic anhydride than do some of the primary amino groups. Acetylation lowers the thermal transition temperature (Tm) of phi W-14 DNA, confirming that the unusually high Tm of this DNA is due to the charged putrescinyl groups, but it does not affect the buoyant density. The extent of lowering of the Tm is proportional to the degree of acetylation. Since some of the secondary amino groups are acetylated before some of the primary amino groups, the effect of acetylation on the Tm suggests that both the primary and secondary amino groups can neutralize negative charge repulsion in phi W-14 DNA. Only the putThy residues in the DNA are modified by TNBS and acetic anhydride.
噬菌体phi W-14 DNA含有超修饰的嘧啶α-腐胺基胸腺嘧啶（putThy）[克罗平斯基，A.M.B.，博斯，R.J.，&沃伦，R.A.J.（1973年）《生物化学》12卷，第151页]。腐胺基侧链的伯氨基与三硝基苯磺酸（TNBS）反应，但反应速率比蛋白质中具有反应活性的赖氨酸侧链慢得多。腐胺基侧链中的伯氨基和仲氨基都能与乙酸酐反应，但在所采用的条件下反应不完全。一些仲氨基与乙酸酐的反应比一些伯氨基更快。乙酰化降低了phi W-14 DNA的热转变温度（Tm），证实了该DNA异常高的Tm是由于带电荷的腐胺基，但它不影响浮力密度。Tm降低的程度与乙酰化程度成正比。由于一些仲氨基在一些伯氨基之前被乙酰化，乙酰化对Tm的影响表明伯氨基和仲氨基都能中和phi W-14 DNA中的负电荷排斥。DNA中只有putThy残基被TNBS和乙酸酐修饰。
