Functional cis-element sequence requirements for suppression of gene expression by the TNPA protein of the Zea mays transposon En/Spm

TNPA, one of the two transposition proteins encoded by the En/Spm transposable elements of Zea mays, suppresses the expression of genes that contain an appropriate cis element. Suppression can be monitored in tobacco protoplasts in a transient expression assay as follows. The plant promoter-driven expression of the Escherichia coli-glucuronidase (GUS)-encoding gene, uidA, is repressed in the presence of TNPA if the GUS gene contains a functional cis element in the untranslated RNA leader sequence. Earlier, we found that the minimal cis element is composed of two 12 by sequences in a tail-to-tail inverted orientation. Each 12 by sequence is sufficient to bind TNPA in vitro and can be thought of as a half-site in the cis element. Here, we investigated the sequence requirements of the minimal cis element. Our observations support our expectations that a functional cis element must provide a template to which two TNPA molecules can bind in the correct orientation. Sequences within the half-sites can be altered as long as the eight bases that make up the consensus binding sites are not changed. However, we found the following unexpected sequence specificities. Firstly, some changes to the consensus binding sequence can be tolerated in one half-site, as long as the other site matches the consensus. Secondly, although the region between the half-sites can vary in sequence and in length between two and four bases, a thymidine residue is not tolerated directly 5′ preceding the second half-site. Since many variants of the cis element sequence remain functional, the suppressor response element provides a flexible tool for artificially manipulating the expression of genes.     

Governing equations of motion for the otolith organs and their response to a step change in velocity of the skull

The otolith organs are the linear motion sensors of the inner ear. They comprise an overdamped second-order system and respond to gravity and skull acceleration. The governing equations of motion which describe the relative displacement of the mass with respect to the skull are developed. When these equations are non-dimensionalized they indicate that the elastic term is almost negligible with respect to the viscous and inertial terms. For a step change in skull velocity an analytic solution is given for the elastic term equal to zero and numeric solutions are given for small values of the elastic term.     

Effects of polyamines on the first division cycle of Xenopus laevis eggs

The involvement of polyamines in cytokinesis has been examined in eggs of the amphibian X. laevis. Microinjection of spermine or spermidine into unfertilized eggs induced a shortening of the first division cycle and early formation of cleavage-like constrictions. Eggs were activated by injection and developed furrows about 45 min later, whereas the first division normally occurred around 120 min after activation. In terms of concentration, spermine was slightly more effective than spermidine, but putrescine had no influence on the division cycle.     

Plant regeneration from cotyledonary tissue of Glycine canescens,a perennial wild relative of soybean

Cotyledonary tissue from immature embryos of Glycine canescens was induced to callus and then form embryo-like structures. These structures could be cultured into whole plants and grown in soil.     

Selected aspects of collared peccary (Dicotyles tajacu) reproductive biology in a captive texas herd

Collared peccaries (Dicotyles tajacu) from 32 litters were born in captivity during the period from September, 1981 through July, 1983. Incidence of singleton, twin, and triplet litters was 28%, 66%, and 6%, respectively. Mean (± SE) weight of young from singleton, twin, and triplet litters was 751 (± 35) gm, 698 (± 17) gm, and 612 (± 74) gm, respectively. Sex ratio among all litters was 56:44 (M:F). Neonatal mortality amounted to 9% of the young born. Mean duration of estrus was 2.60 days and mean length of gestation was 145.6 days. Evidence indicated that multiple copulations increased ovulation rate and the chance for conception.