Many viruses that infect eukaryotic cells express genes that alterthe regulation of host gene expression to promote viral replication.For example, herpes simplex virus-1 (HSV-1) expresses aprotein called ICP0, which is necessary for successful viral infectionand replication within the host. Lutz et al. (2017. Viruses9: 210) showed that ICP0 can act as a ubiquitin ligase and targetthe redundant transcriptional repressors ZEB1 and ZEB2,which leads to upregulation of the miR-183 cluster (a set of threemiRNAs transcribed from the same locus). Speculate on how miR-183 cluster upregulation may benefitthe virus.

The symbols a, b, and c in the table below represent theE. coli lac system genes for the repressor (I ), the operator(O) region, and the β-galactosidase (Z), although notnecessarily in that order. Furthermore, the order inwhich the symbols are written in the genotypes is notnecessarily the actual sequence in the lac operon.Activity (+) or inactivity (−) of Z geneGenotype Inducer absent Inducer presenta- b+ c+ + +a+ b+ c- + +a+ b- c- - a+ b- c+/a- b+ c- + +a+ b+ c+/a- b- c- - +a+ b+ c-/a- b- c+ - +a- b+ c+/a+ b- c- + +a. Which symbol (a, b, or c) represents each of the lacgenes I, O, and Z ?b. In the table, a superscript minus sign on a gene symbolmerely indicates a mutant, but some mutant behaviorsin this system are given special mutant designations.Using the conventional gene symbols for the lac operon,designate each genotype in the table.

Describe what would happen to the lac operon in a low-lactose environment and in a high lactose environment. a) How will each of these environments affect gene expression? b) What would happen to the repressor in each case? c) How will each of these environments affect RNA polymerase?

Name a nucleoside analog. Explain how that nucleoside analog works. Which viruses are effectively treated by that nucleoside analog?