Question

Cascade regulation is a mechanism for controlling the timing of gene expression involving multiple operons. Give an example of cascade regulation and use this example to explain its basic principle

Answer 1

Cascade controlling means controlling gene expression. Many genes encode transcription factors that, in turn, induce the expression of other transcription factors, thus creating cascades of gene expression wherein a multistep signaling pathway results in amplification of the initial signal.

3 regulatory classes of vaccinia virus genes — early, intermediate and late — have distinctive promoters and stage specific virus-encoded transcription factors. The expression of vaccinia virus early genes occurs soon after the cell gets infection and virus enters tinto the cytoplasm. The core associated RNA polymerase, VETF, capping and methylating enzymes, and poly(A) polymerase produce viral transcripts that resemble eukaryotic mRNAs in structure and are translated efficiently. The products of the early mRNAs include RNA polymerase, capping enzyme, and poly(A) polymerase subunits, DNA polymerase and factors for specific transcription of intermediate genes. The virion DNA cannot serve as a template for intermediate gene expression, probably because core proteins restrict access by the newly synthesized transcription complex. Following DNA replication, however, intermediate genes are transcribed. The products of the intermediate genes include three transactivators of late gene expression. In the third phase of the cycle, the late genes are expressed and virion enzymes, early transcription factor and structural proteins are assembled into infectious progeny viral particles to begin the cycle again.