Expression of cis-regulatory mutations of the white locus in metafemales of Drosophila melanogaster.

At the white eye colour locus, there are a number of alleles that have altered expression between males and females. To test these regulatory mutations of the white eye colour locus for their phenotypic expression in metafemales (3X; 2A) compared to diploid females and males, eleven alleles or transduced copies of white were analysed. Two alleles that exhibit dosage compensation between males and females (apricot, blood) also exhibit dosage compensation in metafemales. White-ivory and white-eosin, which fail to dosage compensate in males compared to females, but that are distinct physical lesions, also show a dosage effect in metafemales. Two alleles with greater expression in males than females (spotted, spotted-55) exhibit even lower expression in metafemales. Lastly, five transduced copies of white carrying three different lengths of the white promoter, but that all exhibit higher expression in males, show reduced expression in metafemales, exhibiting an inverse correlation between the level of expression and the dosage of the X chromosome. Because these alleles of white respond to dosage compensation in metafemales as a continuum of the male and female responses, it is concluded that the same basic mechanism of dosage compensation is involved and that the dosage of the X chromosome conditions the sexually dimorphic expression.     

The polyelectrolyte properties of elastin.

The charge structure and ionic interactions of elastin prepared from the pig thoracic aorta by acid, alkali, or CNBr extraction have been investigated by potentiometric titration and radiotracer techniques. The number of charged groups was consistent with the amino acid composition, comparable to elastin from other sources and insensitive to the method of preparation. The enthalpies of ionization of the basic groups were comparable for those previously found for proteins but those of the acidic groups were higher. Ionic interactions were predominantly electrostatic although a strong affinity for chloride ions was noted. Changes in ionic interactions as the elastin was stretched had a similar effect to an increase in the apparent fixed charge density of the tissue. Mechanical strain altered the protonation of the elastin and the pK of the carboxyl groups. Conversely, the conformation of the elastin network varied with ionic strength and pH, being particularly sensitive to the degree of ionization of the more basic groups and with the ionic strength and anion composition of the medium. We speculate that strain induced changes in the conformation of elastin altering its reactivity towards lipids, ions or matrix macromolecules or changes in its mechanical properties resulting from changes in its ionic environment may be of physiological or pathological importance.