Transposon tagging can work. Even though most of our understand­ ing about the factors that contribute to a successful tagging experiment has been accumulated from a limited number of experiments using different transposable elements in different genetic backgrounds, it is still possible to draw some conclusions regarding the best experimental strategies for gene tagging. In our experience, Spm has proved to be a good element for transposon tagging. The frequency of recovering mutable alleles in­ duced by Spm is not significantly different from that for Ac-Ds or for Mu 6 (summarized in Ref. 22) and varies from about 10- to 10=zr:-8pm has the unique advantage, however, in that all of the members of thiSfumily that have been examined thus far are homologous to each other at the DNA level. Therefore, by combining molecular analysis with genetic segre­ gation, it is possible to identify and isolate alleles that are due to insertions of either autonomous or nonautonomous Spm elements. There are definite steps one can take to increase the chances of de­ tecting a transposition into the gene of interest. The most important step is to select a genetic background in which the desired phenotype will be easy to screen. If the phenotype is not likely to be mutable, then tester lines should be constructed so as to contain flanking markers that can aid in subsequent segregation analyses.

Inhalt

Positive and Negative Regulation of the Suppressor-Mutator Element.- Germ Line and Somatic Mutator Activity: Are They Functionally Related?.- The Mobile Element Systems in Maize.- Genetic and Molecular Analysis of Transposable Elements in Antirrhinum Majus.- Recombinant Mutable Alleles of the Maize R Gene.- Studies on Transposable Element Ac of Zea Mays.- Maize Transposable Elements: Structure, Function, and Regulation.- Structure and Function of the En/Spm Transposable Element System of Zea Mays: Identification of the Suppressor Component of En.- Regulation of Mutator Activities in Maize.- The Use of Mutator for Gene-Tagging: Cross-Referencing Between Transposable Element Systems.- Advantages and Limitations of Using Spm as a Transposon Tag.- Transposition of Ac in Tobacco.- Transposition and Retrotransposition in Plants.- The Maintenance of Transposable Elements in Natural Populations.- Deletions and Breaks Involving the Borders of the Ac Element in the bz-m2(Ac) Allele of Maize.- Transposable Elements of Antirrhinum Majus.- The State of DNA Modification Within and Flanking Maize Transposable Elements.- Extrachromosomal Mu.- Molecular Characterization of Suppressor-Mutator (Spm)-Induced Mutations at the bronze-1 Locus in Maize: The bz-m13 Alleles.- Mutagenesis Using Robertson's Mutator Lines and Consequent Insertions at the Adhl Gene in Maize.- A New Mu Element from a Robertson's Mutator Line.- Alterations in Gene Expression Mediated by DNA Insertions in the waxy Gene of Maize.- Discovery of Ac Activity Among Progeny of Tissue Culture-Derived Maize Plants.- Activation of Silent Transposable Elements.- Activation of a Mutable Allele in Alfalfa Tissue Culture.- Structure and DNA Modification of Endogenous Mu Elements.- Comparison of Methylation of the Male- and Female-Derived wx-m9Ds-cy Allele in Endosperm and Sporophyte.- Contents: Poster Abstracts.- Poster Abstracts.- Participants, Chairmen, and Speakers.