Incomplete dosage compensation in an evolving Drosophila sex chromosome

Cellular autoradiography was used to measure relative rates of chromosomal RNA synthesis and to examine the regulatory phenomenon of X-linked dosage compensation in Drosophila miranda, a species containing two distinct, nonhomologous X chromosomes (X1 and X2). The X1 chromosome was found to be dosage-compensated, since the rate of RNA synthesis along the single X1 chromosome in males equaled that of both X1 chromosomes in females. Unlike other sex chromosomes that have been studied, the more recently evolved X2 heterochromosome exhibited regional differences in transcriptional activity when males and females were compared. The distal 10% of the X2 was not dosage-compensated, whereas the majority of an interior segment, representing 30% of the X2 chromosome's length, was found to be dosage-compensated. Our data are consistent with the idea that the evolution of X2 dosage compensation has paralleled the differentiation of the X2 sex chromosome. In addition, gene rearrangement seems to have accompanied the acquisition of a dosage-compensory mechanism in the X2.

Heterogeneity of the ribosomal genes in mice and men

The structures of mouse and human ribosomal DNA were studied using the restriction enzymes Eco R1 and Hind III. Individual mice or humans showed a heterogeneous pattern of restriction fragments resulting from differences in the non-transcribed spacer DNA. Six individual mice from the inbred strain CBA/H-T6 had identical patterns. The same pattern was shown by another CBA strain and by C3H. These strains were originally derived from a BALB X DBA cross made in 1920. Different patterns were found for BALB/c, C57BL and Mus poschiavinus. Cultured cells derived from C3H mice (L cells) showed a pattern quantitatively different from that of the parent strain, but two myeloma cell lines derived from BALB/c showed the same pattern as BALB/c mice. Ribosomal DNA in man is also heterogeneous. Differences were observed between human DNAs in the amounts of the different spacer classes. Studies on mouse-human cell hybrids suggest that some spacer classes are present on more than one of the five human nucleolus organizers.

Preparation of specific antisera to Drosophila acid phosphatase without rigorous protein purification

Extracts from an acid phosphatase CRM- null mutant of Drosophila melanogaster were used to eliminate contaminating antibodies in a nonspecific preparation of anti-acid phosphatase serum. This method of producing specific antisera makes unnecessary the rigorous purification of an antigen prior to immunization attempts in those cases where CRM- null mutants of the antigen are available. Antisera so prepared could be used for a wide variety of purposes.

Isozymes of lysozyme in leukocytes and egg white: evidence for the species-specific control of egg-white lysozyme synthesis

Two structurally distinct forms of eggwhite lysozyme (EC 3.2.1.17) are known. The egg white of some species contains both of these forms, while the egg white of other species appears to contain only one or the other of them. We have immunological and electrophoretic evidence that the chicken, which has only one lysozyme type in its egg white, contains both types in its polymorphonuclear leukocytes. Experiments on Embden goose bone marrow showed that this tissue also contains both lysozymes, even though the egg white of this species contains only one of them. Our studies suggest that many avian species have the genetic loci that code for both forms of lysozyme, but that a species-specific regulatory mechanism controls whether one or the other or both of them are expressed during egg white production. The fact that two distinct lysozymes are present in chicken leukocytes may be of significance to the antibacterial mechanism of these cells, especially in light of the fact that they lack myeloperoxidase, an important leukocyte enzyme in mammals.

Molecular size of hagfish muscle lactate dehydrogenase

In contrast to an earlier report, we find that the primitive vertebrate Eptatretus possesses a muscle lactate dehydrogenase whose molecular size is like that of lactate dehydrogenases from higher vertebrates. The molecular size of lactate dehydrogenase appears to have remained constant during evolution.