In some instances, insertion of maize transposable elements into exons does not result in the total loss of enzymatic activity. In other instances, messenger RNAs of wild-type size are encoded by genes known to contain the maize transposable element Dissociation (Ds) in exons. To understand how Ds is processed from RNA, a study was made of transcripts encoded by two alleles of the maize waxy (wx) gene containing Ds insertions in exon sequences. The analysis was carried out in strains where the Ds element could not excise from the wx gene. Despite insertions of 4.3- and 1.5-Ds elements, the predominant transcripts encoded by these two genes were wild type in size. For both alleles, DNA sequencing of complementary DNAs revealed that the Ds elements had been spliced in a similar manner. Splicing was accomplished by the utilization of multiple 5' donor splice sites in the Ds termini and a 3' acceptor site within the wx gene adjacent to the Ds element. The net effect in both cases was the removal of most of the Ds element from the messenger RNA.

The waxy (wx) locus of maize encodes an enzyme responsible for the synthesis of amylose in endosperm tissue. The phenotype of the Dissociation (Ds) insertion mutant wx‐m1 is characterized by endosperm sectors that contain different levels of amylose. We have cloned the Wx gene from this allele and from two germinal derivatives, S5 and S9, that produce intermediate levels of amylose. The Ds insertion in wx‐m1 is in exon sequences, is 409 bp in length and represents an example of a class of Ds elements that are not deletion derivatives of the Activator (Ac) controlling element. The two germinal derivatives, S5 and S9, lack the Ds element but contain an additional 9 and 6 bp, respectively, at the site of Ds insertion. The level of Wx mRNA and Wx protein in S5 and S9 is essentially the same as in normal endosperm tissue but Wx enzymatic activity is reduced. Thus, the lesions in S5 and S9 lead to the addition of amino acids in the Wx protein, resulting in Wx enzymes with altered specific activities. This work supports the notion that the maize transposable elements may serve a function in natural populations to generate genetic diversity, in this case, proteins with new enzymatic properties.

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SynopsisMixtures of bacteriophage T4D particles with up to six tail fibers attached were separated and analyzed in a quasielastic light scattering-band electrophoresis apparatus. The electrophoretic mobilities and diffusion coefficients of the separated bands were determined during the same experiment. Species differing in mobility by 0.05 X lov4 cm*/V sec were resolved. Henry's electrophoresis theory for spheres indicates that each tail fiber contributes about 240 effective positive charges to the phage structure. Estimate of the charge using the permanent dipole moment and the electrophoretic mobility (Bontje et al. (1977) Riopolyrners 16,551-572) gives an effective charge of +230 to +250 per tail fiber. The charge distribution on the fiberless particles was estimated to be -3380 on the head and -290 on the tail if the dipole moment was assumed positive and -1400 on the head and -1000 on the tail for a negative dipole. Tail-fiber attachment does not proceed to completion in our in uitro system, as substantial quantities of the intermediate species are always present. Analysis of the population distributions as a function of tail-fiber input indicates the reaction is a random, noncooperative process.

Two maize inbred lines harbor non-mutant waxy (Wx) genes that display restriction fragment length polymorphism (RFLP) upstream from the start of Wx transcription. Sequencing of this region in the two strains revealed a DNA insertion with the structural features of a transposable element. The insertion is 316 bp in length, has 15 bp imperfect inverted repeats and is flanked by a 5 bp direct repeat generated upon insertion. Sequences homologous to this insertion are present in multiple copies in maize and its relatives teosinte and Tripsacum but not in the more distantly related dicot tobacco. Finally, this element is not homologous with any previously described maize DNA insertion.