A system for mapping DNA sequences in the chromosomes of Drosophila melanogaster.
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Biomedical subjects
Publications and source records attributed to D S Hogness.
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The replicating chromosomal DNA in Drosophila melanogaster cleavage nuclei has been visualized in the electron microscope as a serial array of closely spaced replicated regions created by pairs of diverging replication forks. The fine structure of the forks is very similar to that observed for the replication forks of bidirectionally replicating bacteriophage DNAs. However, the mean length of the single-stranded gaps in Drosophila forks is less than 200 nucleotide residues, much shorter than the gaps in phage forks. This difference in gap length corresponds to the observed difference in the size of Okazaki fragments from Drosophila and phage.
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The position and orientation of genes in lambda and lambda dg DNA are described. The position of six genes located in the right half of isolated lambda DNA was found to be -(N, i(lambda))--O-P---Q-R-(right end of DNA), which is their order on the genetic map of the vegetative phage. The order of the three genes of the galactose operon (k, t, and e) located in the left half of lambda dg DNA was found to be (left end of DNA)----k-t-e-, consistent with Campbell's model (5) for the formation of this variant. Gene orientation, defined as the direction of transcription along the DNA, is inferred to be from right to left for the galactose operon in lambda dg DNA. The strand of lambda DNA which functions as template in transcription of N, an "early" gene required for normal replication of lambda DNA, was determined as a first step in ascertaining the orientation of this gene. The method includes isolation of each strand, formation of each of two heteroduplex molecules consisting of one strand from wild-type and one from an N mutant) and comparison of their N activities. The second step, which consists of ascertaining the 5'-to-3' direction of each strand, is discussed, as is a determination of the orientation of gene R.
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The Ubx and bxd transcription units comprise a single functional domain in the bithorax complex of Drosophila melanogaster. The segmental distributions and nuclear localization of proteins encoded by the Ubx unit have been determined by immunofluorescence staining with antibodies raised against a fusion protein containing Ubx coding sequences. Wild-type and mutant distributions are consistent with a model in which the protein-coding functions of the domain derive from the Ubx unit and are regulated by the bxd unit.