406 



CHAPTER 44 



' 5 NH^ 10 15 



Acetyl N-Ser*Tyr— ►•Sef-»'lleu— *'Thr-»-Thr— ►Pro— »-Ser-»>Glu-»>Phe-*'\tal-»-Phe-»Leu-*>Ser-».Sef -^^ 



30 NH^ 25 NH^ 20 ) 



CAIa-*— Asp'*— Thr'*— CySH^-Asp-*— Leu'^-lleu-* — Leu-^— Glu-< — //e<j<— .='ro-«-/Qs/=>'<»->a/o-«— Try« — Alo ^ 

 NH^ NH^ 35 NH^ NH^ NH^ 40 ^^ NH^ 45 



Leu-^Gly— ♦Asp-*Glu— ►Phe— >Glu — ►Thr— ♦Glu— ♦Glu — ►Ala— •(Arg)— ►Thr— ►Vol— ►Glu— ♦Vbl ■^^ 



60 NH^ 55 50 /V//, NH^ ) 



CVol"*— Thr<— Val-< — Glu-4-Pro-«— Ser^-Pro-* — Lys-<— Try<— Val-<— Glu-«— Ser-«— Phe-»-Glu*-(Arq) V 

 (Ar^Phe-^Pro — ►Asp-»-Ser— ►Asp-^Phe— »{Lys)— ►Vol — ►Tyr— »^^)— ►Tyr— ►Asp— ►AlG-*Val ->. 



.90 85 80 ) 



C(Arqi)«— Thr-«— Asp-*— Phe*-Ala-*— Gly •♦- Leu-«— Leu^-Ala*— Thr<«— Vol-*— Leu*-Pro-*— Asp *— Leu V 



C 



^— -. 95 NH^ IVMp Nflp lOU /V/^ I 



Asp-MArg)-^|leu — ►lleu-^GIu — ►Val->-Glu — ►Asp-^GIu— ►Alo— ►Asp-^Pro— ►Thr— ►Thr— ».Ala -^ 

 Ala-«— Vol-*— Thr-< — Ala-4-Asp-*-Asp-#-Val-* — Arg-<-(Ar^>«— Thr-*— Ala<»-Asp-*-Leu-«— Thr-<— Glu 4r 



^— V 125 /V//o 130 _ i^s 



lleu- 



-■ 115 ^-.^ 110 



)<— Vol'* — Thr-* — Ala-*—Asp<— Asp*-Val'* — Arg-«-(Arq>«— Thr-*— Ale-*— Asp^-Leu-*— Thr-«— Glu 



/ir\ ^ '^^ '^"^ 130 ^_- 135 



J— ►(Ar^)-^5er — ►Ala— ►Asp— ►lieu— ►Asc-^/«i^—^//ec/— ►vo/— ►G/t^ -►Leu —►lieu — »(Arg)-^GIy 



150 



CLeu*-biy«— ser-* — Ser-«-Ser-*— Glu-*-Phe*- 

 155 

 Vol— ►Try— ►Thr— ►Ser-*Gly— ► Pro-^AIa— ► 



140 fi/M^ 



Leu'^-Gly'*— Ser-* — Ser-«-Ser-*— Glu-*-Phe*-Ser.«— Ser<-^ra)#— Asp. 



Leu— ►lieu — •^Arm— »oiy -v 

 Tyr.«— Ser-*— Gly«— Thr V 



FIGURE 44-4. Amino acid sequence in the protein building block of the tobacco mosaic 

 virus {TMV). There are 158 amino acids in the sub-unit, the encircled residues indicate 

 the points of splitting by trypsin. {Courtesy of A. Tsugita, D. T. Gish, J. Young, 

 H. Fraenkel-Conrat, C. A. Knight, and W. M. Stanley, Proc. Nat. Acad. Sci., U.S., 

 46:1465, 1960.) 



infectivity of the original virus. Using two 

 genetically different strains of this virus, the 

 standard (TMV) and Holmes rib grass (HR), 

 it is possible to construct a highly infective 

 virus containing the RNA of TMV and the 

 protein coat of HR. The progeny obtained 

 are typically TMV with respect to RNA and 

 protein coat. The reciprocal construct, a 

 virus with HR RNA and TMV protein pro- 

 duces typical HR progeny in both their RNA 

 and protein. Thus, // is only the RNA of a 

 TMV particle which specifies the RNA and 

 protein of the progeny virus. ^^ 



Mutations can be induced in TMV RNA 

 by many of the agents which are mutagenic 

 for DNA. For example, deamination of 

 single bases by nitrous acid is mutagenic. 



" The genetic experiments described for TMV are 

 based largely upon work of H. Fraenkel-Conrat and 

 R. C. Williams (1955), A. Gierer (1960), G. Schramm, 

 and others. 



Such results and others prove that the bio- 

 logical activity of the RNA depends upon its 

 primary (nucleotide content) and not its 

 secondary (coiling pattern) structure. 



The results mentioned prove that RNA is 

 the genetic material in RNA-containing vi- 

 ruses. While the genetic information is 

 carried by a single strand of ribotides within 

 the RNA virus, we do not have any clear 

 evidence with regard to the mode of replica- 

 tion or of function of the RNA once it is 

 inside its host. It may be noted, in the case 

 of 0X174, whose DNA resembles RNA in 

 being single-stranded, that there is some evi- 

 dence suggesting that its replication involves 

 the formation of a complementary DNA 

 chain, which, however, does not become in- 

 corporated into mature phage. Even if the 

 formation of a complementary chain proves 

 to be true for this phage, it still remains to be 

 seen whether this also occurs during the 

 replication of RNA genetic material. 



