THE JOHN CURTIN SCHOOL OF MEDICAL RESEARCH THE AUSTRALIAN NATIONAL UNIVERSITY CANBERRA, A.C.T. Telegraphic Address: seer t “Natuniv” eww a Telephone: U 0422 eend January, 1959. Dr. J. Lederberg, Department of Genetics, Stanford University, Palo Alto, CALIFORNIA, U.S.A. Dear Josh, I am writing to ask your advice on symbols for the characters of vaccinia virus. I think that we have now reached the stage where a proper genetic study of this virus is possible, though still laborious and inaccurate when compared with phage. It is important that terminology should be straightened out now, for the retention of a lab jargon such as Burnet uses for flu makes comprehension of papers difficult (as I know as a reader of his papers!). The position at present is that with two different strains of virus we have unequivocal evidence of recombination affecting a number of different characters (Virology 1958, 5, No. 3, 530). Since then I have obtained a similar range of recombinants from single mixedly infected cells, isolated in microdrops. The weakness of this approach was that the two parental types differed in a whole range of unknown markers as well as those we looked at. We now have a way out of this by using the "white variants" of strains which produce red pocks on the chorioallantoic membrane. Study of a number of white variants of rabbitpox shows that they are genetically different (they differ in other characters than "whiteness", and they recombine with high frequency to produce wild type). Thus we should, during the coming year, be able to press on with our study of the genetic structure of vaccinia virus (to which "rabbitpox" belongs) using different mtants of one parental strain. The characters with which we have so far been concerned, and my suggested symbols for them, are as follows:- THE JOHN CURTIN SCHOOL OF MEDICAL RESEARCH CONTINUATION Ze (1) (2) (3) Pock character on the chorioallantoic membrane. A complex character involving the response of the chick embryo as well as the multiplication characteristics of the virus. The broad division is into "red" and "white" pocks,. My suggestion is w (for "white") w is the "red" wild type Wy to Ww, are "white" mutants, of which there are a great number, An alternative, which may be preferable, would be to equate "red" with "ulcer" and "white" with "non-ulcerated lesion", We would have u* = wild type (ulcerated lesion) uy to u,= "white" mtants, non ulcerating. The advantage is that one doesn't use a contradictory symbol like we for a red pock; but u’ for ulcerated and u for non-ulcerated. Plague character on chick embryo fibroblasts. Wild type (w’) strains produce large plaques. Various w mutants produce smaller plaques, or plaques with irregular edges, or plaques the same size as wt, I suppose the appropriate abbreviation would be similar to that used by phage geneticists: i.e. "m" "fu" for fuzzy, etc. (One difficulty here is that certain white mtants produce minute plaques, ise. they are probably two expressions of one mtation.) Haemagelutinin production. Sometimes this antigen is not produced: a’ = wild type; haemagglutinin produced (a = agglutinin). a =» mutant which fails to produce haemagelutinin. There may be quantitative differences amongst the tigtn if measured under standard conditions relative to number of infectious particles, or total particles. (The vaccinia HA is separable from the virus particle.) THE JOHN CURTIN SCHOOL OF MEDICAL RESEARCH CONTINUATION 3%, (4) (5) Heat Resistance. t* = wild type - temperature resistant (i.e. under standard conditions drops about 1 log in 40' at 55°C) t = temperature sensitive variant (drops 4-5 logs in 40! at 55°C). Among some 200 recombinants I haven't yet found any intermediates. Virulence characters. In intact animals these are obviously complex and under polygenic control. I do not propose to use them in the early stages of work on the genetics of vaccinia, but these will ultimately be important. In addition we have to consider ability to multiply (or produce plaques) in various types of cell. These are essentially host range characters, so might be grouped as "h" characters. Mouse virulence would then be: hm = high virulence from the mouse (after I-C injection) hm) to hm = virulence from the mouse varying from hn, (There are several levels of virulence but only extremes can be handled. ) Rabbit virulence would be: » , in hr = high virulence (large lesion) fem the rabbit, after intradermal injection. hr) to hr = varying lower levels of virulence. For current work I need to group mouse and rabbit virulence as high, low (-), and intermediate (i), though I am aware that there are quite a number of different "intermediates"; i.e, I would only use the expressions: hm, hm” and hm* hr, hr and hr’. THE JOHN CURTIN SCHOOL OF MEDICAL RESEARCH CONTINUATION 4, For cell lines: ability to produce plaques on "L" cells ability to produce plaques on KB cells hKB ncr* . ability to produce plaques on chick fibroblasts. hcF’ ) nH ) _ ability to produce plaques on HeLa cells. hH Depending upon how completely a strain has been characterized, and what characters are relevant, the virulence characters might be grouped thus: h (mr Lt xKBt cF H-). As we go along, of course, other characters will crop upe What I am concerned with is to get started with reasonable expressions - once that has been done it should not be too difficult to keep it up. I hope you enjoy your new venture at Stanford. With best wishes. Yours sincerely, Frank Fenner.