In vitro studies of protein synthesis in drosophila

Genetic and environmental control of a continuous trait,Abnormal abdomen, inDrosophila melanogaster

The mutant phenotypeAbnormal abdomenis under the control of a major gene,A53glocated distally on theXchromosome. The phenotypic abnormalities are a result of the developmental interaction between this major gene and a modifier system associated with the residual genotype. The primary developmental effect of this mutant genotype is an interference with adult histoblast differentiation resulting in a raggedness or loss of tergite material due to the changes in the formation of the adult abdominal hypoderm. A secondary effect is an interference with middorsal fusion of the histoblasts.

The developmental effect of the genotype is influenced by a number of factors which include crowding, humidity, temperature, and the age of the culture. The mutant phenotype is due to an interaction of the major gene and the modifier system in association with these environmental factors. Gene action in relation to the final phenotype is postulated to be a two-step affair. The first is an increase in protein synthesis under the influence of the modifier system; and the second is the reaction of the histoblast, under the influence of the major gene, to this increase in protein synthesis during its differentiation into adult hypoderm. The function of the environment in this sequence of developmental reactions is postulated to be in its control of the utilization of the increased protein associated with the action of the enhancer genes. This hypothesis is discussed in terms of (1) the production and utilization of gene products and of (2) the regulation of development in terms of this production and utilization in a balanced developmental system.

Cell-free translation in lysates from Spodoptera frugiperda (Lepidoptera: Noctuidae) cells

1. Conditions for in vitro translation of mRNA in cell-free extracts from cultured Spodoptera frugiperda cells were defined. 2. Incorporation of [35S]methionine into acid-precipitable material increased for approximately 1 hr, and was sensitive to the protein synthesis inhibitors pactamycin and cycloheximide. 3. Micrococcal nuclease-treated lysate, primed with purified rabbit globin mRNA, synthesized a major protein with the size of full length globin, indicating that the lysate supported correct initiation and elongation of polypeptides.

Patterns of amino acid incorporation in long-lived genetic strains of Drosophila melanogaster

This study examined the age-dependent alterations in the in vivo incorporation of labeled amino acids into protein during the adult life spans of males and females obtained from genetically based long-lived and control strains of Drosophila melanogaster. All four groups tested showed significant decreases (ca. 50%) in the uptake of labeled amino acids as a function of age. Each of the four groups had their own characteristic temporal pattern of functional decrement. Both the long-lived and the control females have similar patterns of amino acid incorporation, but the onset of these changes is delayed by 10 to 20 days in long-lived animals. These alterations in protein synthesis appear to be related to corresponding changes in the female fecundity patterns of each strain. The male patterns differ from one another and from the female patterns, but they both show periods of high fluctuation early in life followed by a terminal period of relatively low and constant synthesis. These data are consistent with the view that the overall alterations in the longevity of these two strains are likely due to changes in the timing of particular events in the adult life cycle.

Effects of age on the post-initiation stages of protein synthesis

The peptide chain elongation stage of protein synthesis in Drosophila melanogaster was found to decrease markedly with age. The decrease paralleled the age-related decrease in overall protein synthesis. In contrast, the termination stage showed little decrease until the organisms were very old. Of the three reactions that comprise peptide chain elongation, the binding of aminoacyl-tRNA to ribosomes decreased greatly with age, and the decrease paralleled that of peptide chain elongation and of overall protein synthesis. The peptidyl transfer reaction decreased moderately, and the translocation reaction exhibited no measurable decrease with age. Thus, decreased binding of aminoacyl-tRNA to ribosomes appeared to be a major contributor to the age-related decreases in peptide chain elongation and overall protein synthesis.

The effect of age on the initiation of protein synthesis in Drosophila melanogaster

Polyribosome levels exhibited a marked, age-related decrease in adult Drosophila melanogaster. Since decreased polyribosome levels can be due to decreased initiation of translation, initiation was measured by determination of methionyl-tRNA binding to the 40 S and 80 S initiation complexes. Compared with 1-day-old adults, 48-day-old adults exhibited no more than a 12% decrease in methionyl-tRNA binding to 40 S subunits and a 20% decrease in binding to 80 S particles. Increased age, therefore, had relatively little effect on initiation, and the decreased polyribosomal content was probably due to the deterioration of some other component of the translation system.

Stimulatory factor for tRNA aminoacylation: possible product of modifier genes in Drosophila melanogaster

A factor which stimulates the aminoacylation of heterologous and homologous tRNAs for lysine and leucine, as well as a mixture of amino acids, has been isolated from cytoplasmic extracts in Drosophila. The stimulatory factor is separated from inorganic pyrophosphatase activity by DEAE-cellulose chromatography and from aminoacyl-tRNA synthetase activity by trichloroacetic acid precipitation. It contains no nucleotidyl transferase activity. It is trypsin-sensitive and heat-stable, indicating that it may be a small protein. Attempts to measure the molecular weight, however, indicate heterogeneity in size, ranging from 20,000 to 65,000. The A53g mutant has four times as much factor Ore-R adults at 0-2 days; by 6-8 days the level has declined to less than one and a half times that of Ore-R. The heightened aminoacylation activity in the mutant extract is accompanied by increased soluble protein levels. It is known that the stimulation of tRNA aminoacylation in A53g is controlled by modifier genes which enhance the expression of the A53g mutant. The possibility that the stimulation factor is a product of the modifier genes is examined.

Multiple gene control of the tRNA aminoacylating system in Drosophila melanogaster

The stimulation ofin vitrotRNA aminoacylation by post-microsomal supernatant enzymes isolated fromAbnormal Abdomen(A53g) adult flies is a function of the residual genome of these flies rather than of the major mutant gene,A53g. Genes controlling this stimulation are located on theXchromosome as well as on the autosomes. These observations are discussed in terms of the phenotypic effect of the major mutant gene in response to changes in protein synthesis which are under the control of modifier genes responsible for aberrant genetic translation mechanisms.

The effects of inhibition of protein synthesis on the phenotype of Abnormal-abdomen

Penetrance and expressivity of theDrosophilamutantAbnormal-abdomen(A53g) may be reduced by adding inhibitors of protein synthesis, of RNA synthesis, and of oxidative phosphorylation to the defined, sterile medium on which larvae are developing. When grown on regular diet, the mutant flies contain a higher concentration of total protein than do wild-type flies. The metabolic inhibitors which reduce the expressivity of the mutation also lower protein concentration in these mutant flies. The reduction of protein synthesis is directly correlated with the reduction of expression of the mutant genotype. The regulation of the morphological abdominal abnormalities by the complexA53ggenotype is discussed in relation to the control, by this same genetic system, of the mechanisms of protein synthesis.