George Streisinger

A neural degeneration mutation that spares primary neurons in the zebrafish

We describe an embryonic lethal mutation in the zebrafish Brachydanio rerio that specifically affects the viability of most cells in the embryonic central nervous system (CNS). The mutation ned-1 (b39rl) was induced with gamma-irradiation and segregates as a single recessive allele closely linked to its centromere. It produces massive cell death in the CNS but a small set of specific neurons, including Rohon-Beard sensory neurons, large hindbrain interneurons, and primary motoneurons, survive embryogenesis and are functional. Synaptic connections between embryonic motoneurons and muscle cells appear physiologically normal, and the normally observed spontaneous flexions are present. Correlated with the presence of sensory neurons and interneurons, mutant embryos display reflexive movements in response to mechanical stimulation. Together, the surviving neurons, called primary neurons, form a class of cells that are prominent in size and arise early during development. Thus, this mutation may define a function that is differentially required by developmentally distinguishable sets of cells in the embryonic CNS.

Induction of recessive lethal and specific locus mutations in the zebrafish with ethyl nitrosourea

Recessive lethal mutations and mutations at the gol-1 locus were induced in the zebrafish by exposure of mature sperm to the alkylating agent ethyl nitrosourea (ENU). Embryonic lethal phenotypes were recognized among the parthenogenetic progeny of mutagenized animals or among the progeny of daughters of mutagenized animals. Novel specific locus mutations were identified by the failure of mutagenized chromosomes to complement pre-existing mutant alleles at the gol-1 locus. Each mutagenized individual harboured approximately 10 embryonic lethal mutations in its germ line and about 1 in 500 mutagenized animals harboured a new mutation at the gol-1 locus. Three lines of evidence indicate that the majority of mutations that were recovered following treatment of mature sperm with ENU were probably point mutations. First, the soma and germ lines of mutagenized animals were mosaic, as expected following simple alkylation of sperm DNA. Second, mutations induced by ENU at the gol-1 locus affected pigmentation but not viability, unlike the majority of mutations induced at this locus with gamma-irradiation. Third, the ratio of specific locus:recessive lethal mutations induced by ENU was approximately 50-fold lower than the ratio observed following mutagenesis with gamma-rays. Comparison of the incidence with which embryonic recessive lethal mutations were induced with the incidence with which specific locus mutations arose indicates that there are greater than 5000 genes essential to the development and viability of the zebrafish embryo.

The mechanism of lysis in phage T4-infected cells.

Abstract Sensitive bacteria infected with mutant strains of phage T4 that lack active lysozyme do not lyse at the usual time, but oxygen uptake in these bacteria cease at the time lysis would normally occur. Normal lysis seems to be triggered by the cessation of metabolism and is accomplished by lysozyme. Superinfection that causes lysis inhibition prolongs the time during which oxygen uptake occurs.

Induction of mutations in the zebrafish with ultraviolet light.

Recessive lethal germline and specific locus somatic mutations were induced efficiently in the zebrafish by exposure of mature sperm to UV light. Mutagenesis of sperm yielded mosaic individuals: clones bearing novel mutations represented approximately 12-25% of the haploid germ cells and 25-50% of the somatic tissue. Simple methods are described for the reliable identification and propagation of newly arising developmental mutations in zebrafish.

The role of phage lysozyme in the life cycle of phage T4.

The lysozyme that is synthesized under the direction of the e gene of phage T4 is known to cause the lysis of infected bacteria. In this paper we show that this lysozyme plays no detectable role in infection or in lysis from without. We also mention the detection of a heretofore undescribed lytic activity that is associated with mature phage particles.

Frameshift mutations resulting in the changes of the same amino acid residue (140) in T4 bacteriophage lysozyme and in vivo codons for Trp, Tyr, Met, Val and Ile.

Abstract The lysozymes of three new strains of double frameshift mutants of T4 bacteriophage, e J37 e JD3, e J200 e JD4 and e J25 e JD1, were isolated from their respective lysates, and their amino acid sequences were compared with that of the wild-type strain. It was found that Trp 138 -Tyr-Asn 140 in wild-type lysozyme changes to Met-Val-Tyr in e J37 e JD3, Tyr 139 -Asn 140 to Cys-Ile-Ile in e J200 e JD4 and Asn 140 to Ile-Ile in e J25 e JD1. From these results, a new hot spot for frameshift mutations has been found at Asn 140 and in vivo codons for Trp, Tyr, Met, Val and Ile are thought to be UGG, UAU, AUG and AUA, respectively. Nineteen in vivo codons out of 64 codons have been identified by these results together with our previous results.

A frame-shift mutation resulting in the deletion of two base pairs in the lysozyme gene of bacteriophage T4

Abstract The primary structure of the lysozyme of a strain of phage T4 carrying two frame-shift mutations ( e JD5 e J201) has been found to differ from that of the wild-type strain by a sequence of four amino acids. One of the mutations has been shown to be due to the deletion of two bases and the other to the addition of two bases. Frame-shift mutations causing the addition and deletion of single bases and the addition of two bases have been identified previously. The codon GAA has been identified as coding for glutamic acid in the wild-type strain and AGG has been found to code for arginine in the double-mutant strain.

Phenotypic expression of recombinants arising in phage-infected bacteria☆

Abstract Recombinant h genomes, formed in bacteria infected by two different h + mutants, efficiently produced h tail-fiber protein.

ICPEMC working paper 4/2 extrapolations from species to species and from various cell types in assessing risks from chemical mutagens

Strategies for estimating human mutation frequencies can be based on extrapolations of dose: mutation ratios in other species.

Direction of translation of the lysozyme gene of bacteriophage T4 relative to the linkage map

Abstract The lysozyme gene of bacteriophage T4 has been shown to be translated in the same direction as the rII gene and in a direction opposite to that of the head gene. The time of translation of genes of bacteriophage T4 seems not to be determined by the direction of translation.