Question

5. Your professor was playing around with random mutagenesis of a single gene that codes for TFIIH and discovered a strain of fruit flies that displayed significantly slowed developmental rates and low levels of mRNA accumulation in the cytosol. He hypothesized the mutation in TFIIH abolished its ability to hydrolyze ATP. However, after performing ATP hydrolysis reactions with the purified mutant TFIIH protein and ³²P-labeled ATP, he was perplexed to find the rate of ATPhydrolysis was normal in these fruit flies, Given these findings, describe WHERE the mutation in TFIIH likely occurred, HOW the mutation is likely affecting transcription, and WHY mRNA levels in the cytosol is affected.

Answer 1

Transcription factor II H (TFIIH) is actually a protein complex playing an important role in the transcription of genes and aslo help in nucleotide excision repair of DNA. As far as the composition of this transcription factor is concerned, it is composed of 10 subunits with each unit having a particular activity. oout of the 10 units, 2 units are actually required for the initiation of transcription that involve ERCC2/XPD and ERCC3/XPB and these units have two dual activities- helicase activity (required for the formation of transcription bubble by cutting the hydrogen bonds between the complementary DNA strands) and ATPase activity (required for ATP degaradation for helicase activity). As the mutant lines have been found to have normal ATPase activity, it indicates the mutation must be in the helicase domain of the protein. therefore this mutation affects the transcription and also keeps the mRNA levels low.