4 Editorial Notes

One of tile new features is Site Specifics, designed to p rov ide in format ion on plant molecular biologists in d i f ferent ins t i tu t ions and geographical areas. Tristan Dyer has cont r ibuted an example. Well R e pe a t e d Sequences is an a t tempt to i l luminate tile his tory of plant molecular biology. We shall we lcome ei ther articles or brief anecdotes concern ing events of seminal impor tance to tile deve lop- men, of our field. In the future we plan to announce A p p o in tm en t s to p rofessorsh ips and to comparab le posts in research organ iza t ions and also to publish reviews of books in tile area of plant molecular biology.

For a journal devo ted to news and t imely informat ion, ou r most critical concern v, ull be production time. Tile journal ;viii be composed on computers at the editorial office and, th rough the coop- era, ion of our new publishers, Transaction, we expect to be able to ac- cept copy not requir ing review as little as one month in advance of publication. The use of desk-top publishing also permi ts us to accept copy by electronic mad or on f loppy disks (see Ins t ruc t ions to Au- thors), which should both speed tile publicat ion process and improve accuracy,

Finally, the success of our PMBR will be de te rmined in large part by y o u r response as readers and contr ibutors . Tile editorial board and I look forward to an exciting era.

Transposon Tagging

T O a molecular biologist a gene wi thout a gene p roduc t has some- tiling of tile reali ty of the shadows in Plato's cave The first plant genes to be isolated and most of those being isolated to-

day code for abundan t products: rRNAs, RuBisCo, seed proteins, etc. Geneticis ts on the other hand have no such problems: all they re- quire for their con t inued e m p l o y m e n t is a heri table character . We recognize fur thermore that tile p roduc ts of some of the most biologi- call), significant genes, such as those control l ing m o r p h o l o g y or de- \ ' e lopment , m a y accumula te at vanishingly low levels.

When it became possible to isolate and clone mobile genetic e lements , it became ev iden t that the insert ion of a mobi le elernent into a gene would des t roy its funct ion and that, at least in principle, f ragments conta in ing the al tered gene could then be isolated using the cloned e lement as a probe. Reasons were offered w h y the princi- ple would not work in practice: the rate of insert ion of mobi le ele

Cis and Trans 5

ments is too low to be d is t inguished f rom spon taneous mutat ions; lugh copy number s of mobile e lements would make it difficult to de- te rmine which e lement had inser ted into the gene of interest; etc. There are other approaches to the isolation of genes coding for p rod- ucts of low abundance, such as the l inkage of restriction f ragment pol- y m o r p h i s m s with lleritable characters and total sequencing of chro- mosomes, but transposon tagging continues to beckon.

Transposon tagging c a n work.

Rober t Schmidt , Frances Burr, and Benjamin Burr of the Brookhaven National Laborator ies at Upton, N e w York, recent ly re- por ted tile first successful t ransposon tagging of a plant gene, opaque- 2 in rnaize. They did it using tile t ransposable e lement suppressor- mutator (Spin). On tile basis of prior genetic evidence, the p roduc t of opaque-2 is t hough t to funct ion as a pos i t ive t ranscr ip t ion factor. With the gene tagged with Spin, Schmidt et al. were able to c lone the wi ld - type allele and t ranscr ipts were de tec ted wi th no r the rn blots.

Al though Spin has a high copy number in maize, Schmidt et al. were able to ident i fy Spin in opaque-2 by exploi t ing the observa- tion that DNA in the region of active t ransposons is unde rme thy la t - ed. The rate of insertion of Spin may be high, as mobile e lements go, but the Brookhaven g roup found only three posi t ives among 530,000 kernels ha rves t ed f rom three hectares of maize. And two of the three kernels tu rned out to be duds! Other p roblems are that inser- tions show considerable bias for target sites and may be affected by the sex of the paren t bear ing the mobile e lement . Mutable alleles may arise de hove or f rom insert ions of o ther mobile elements. After iden t i fy ing tile n u m e r o u s p rob lems associated with the technique, Cone et al. (1988) declare that, "Transposon tagging can work." f~

- - C . A . P .

References Cone, K C., R.J Schnudt, B Burr & F.A. Burr. 1988 Advantages and limitations of us-

mg Spin a s a transposon tag, in Plant Transposable Elements, O E. Nelson, ed., Ple- num Press, N Y., in p~ess.

Schmldt, R.J, F.A. Burr, and B. Burr. 1987. Transposon taggnng and molecular analys,s of the maize regulatory locus opaque-2. Science 238:960-963

Shepherd, N.S 1987 Transposable elements and gene-tagging, ~n Plant Molecular B~- elegy: A Practical Approach. C. H. Shaw, ed. [RL Press, London