Cells have several mechanisms to prevent the production and accumulation of truncated protein fragments. To illustrate why these fragments can be deleterious, consider a transcriptional activator protein called Groovy that binds to an enhancer element upstream of the Zippy gene. The Groovy has 2 domains, a DNA-binding domain at its N-terminus that binds to DNA at the Zippy gene and a domain that binds a histone-modifying enzyme at its C-terminus. When the second domain binds a histone-modifying enzyme, the histone modifying enzyme alters the chromatin structure at the Zippy gene leading to increased transcription of Zippy.
A. If a cell makes substantial amounts of an N-terminal fragment of Groovy, containing the DNA-binding domain alone, what is likely to happen to transcription of the Zippy gene (increase, decrease or stay the same)?
B. If, in aIDition to the N-terminal fragment of Groovy, a cell also makes an equal amount of the full-length protein, what is likely to happen to transcription of the Zippy gene (increase, decrease or stay the same)?
C. Consider two cell lines or strains that each have a fully functional allele of the Groovy gene on one copy of chromosome 3. On the second copy of chromosome 3, strain 1 lacks a second Groovy allele whereas strain 2 contains the Groovy allele that codes for the N-terminal fragment described in part A. If strain 1 and strain 2 have different amounts of Zippy mRNA, which do you expect to have more Zippy mRNA? Explain.