Dose Compensation of Genes and Transcription

Some of the mutations which change the transcription of ribosomal genes in D. melanogaster are known. However, the mechanisms of these gene actions are not clear. 

The mutation lethal-meander (Ime, 2-71 and 73 Lindsley and Grell, 1967) has an early effect on larval development. This mutation inhibits larval growth and is characterized by a very low concentration of DNA and RNA in the salivary glands, digestive tube, and other organs. The RNA/DNA ratio (2, 2-3, 4) is also reduced as compared to the normal (8.8-10.8). However, 28S and 18S RNA are synthesized with delay. Therefore, this mutation affects only the time of transcription (Chen et al., 1963 Weideli et al., 1969 Kubli, 1970 Chen, 1971 Kubli et al., 1971). 

It was suggested (Chen, 1971) that a similar mechanism of RNA synthesis distortion occurs in the mutant larva lethal giant (Igl, X chromosome, 2,0 + Lindsley and Grell, 1967). 

The dose compensation is an example where the gene interaction in the regulation of the nonribosomal RNA synthesis was demonstrated for various animals and especially Drosophila. 

Differential Activity of Genes as a Basis for Cell Differentiation 

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Korge (1970b) demonstrated that the dose compensation (the 3B puff of Df(l)w y/ strain D. melanogaster was chosen as an experimental niodel) or the dose effect (duplication in female and male) occurs on the transcriptional level (Fig. 14). Although direct comparison was not possible, there is good correlation between the RNA synthesis and the phenotypic expression in the case of the dose compensation as well as in the case of the dose effect, when the trait expression is associated with the gene number. Two results represented the special interest ... 

Therefore, dose compensation is determined by differences in the transcriptional activity of the X chromosome in the male and female and is an example of the well-proven regulation of gene activity in animals. This regulation is apparent in the synthesis on only a certain amount of RNA. Various parts of the chromosome have demonstrated a kind of autonomy in this respect. 

There are few actual experimental data concerning the transcriptional level of gene action regulation and these data are restricted, in general, by observations of the dose compensation mechanism (see above). 

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