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Degree Name

Doctor of Philosophy




The transposable element Enhancer (En), encodes the functions necessary for it to excise and transpose members of the En-I family of transposable elements. Following the molecular isolation of the Waxy (Wx) gene, En containing lines were used to rescue the movement of En into the Wx locus. From these experiments a selected unstable mutant designated wx-844 was isolated (1 in 2 million kernels). Using genetic analysis proof was obtained that an autonomous En element was co-segregating with the wx-844 allele;Genomic Southern blots with DNA from the heterozygous wx-844/wx plant confirmed that an insert of 8.4 kb, displaying somatic excision, was present in the wx-844 allele. The wx-844::En-1 allele was cloned in the (lamda) EMBL4 vector and the insert designated En-1 was shown to be homologous at its termini to the previous cloned I insert at the wx-m8 allele;DNA sequence analysis revealed that En-1 is inserted in an intron of the Wx gene, causes a 3 base pair (bp) target site duplication and possesses a 13 bp perfect inverted repeat at its termini in addition to other inverted and direct repeats which can be formed into a stem and loop structure. En-1 is 8287 bp in length, direct and inverted repeats are localized to about 500 bp of each terminus, and internally contains a 2.5 kb long open reading frame. In lines containing En a major transcript of 2.5 kb and minor transcripts of 6 kb and 1.5 kb observed in Northern blots, are homologous to fragments of En-1;En-homologous sequences are dispersed in the maize genome, and are present at about 40-60 positions in the genome of various members of the genus Zea, possibly as defective I elements. En has been effective in rescuing tagged (with En) genes. Using the characterized En-1 restriction map, specific fragments as probes and mutants containing autonomous En elements, various loci have been cloned by collaborators.



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Andy Pereira



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279 pages