Rpb7 can interact with RNA polymerase II and support transcription during some stresses independently of Rpb4

Area of Science:

• Molecular Biology
• Yeast Genetics
• Transcription Regulation

Background:

• Rpb4 and Rpb7 are subunits of yeast RNA polymerase II (Pol II).
• RPB7 is essential for yeast viability, while RPB4 is important under stress.
• Previous studies indicated Rpb7 stably interacts with Pol II as a heterodimer with Rpb4.

Purpose of the Study:

• To understand the mechanistic role of Rpb4 in yeast Pol II function.
• To resolve the discrepancy between RPB7's essentiality and RPB4's conditional essentiality.
• To investigate how Rpb4 influences Rpb7's interaction with Pol II.

Main Methods:

• Genetic screen for suppressors of rpb4Delta temperature-sensitive growth defect.
• Overexpression of RPB7 and RPB4 in rpb4Delta yeast strains.
• Assessing growth under various stress conditions (heat, cold, starvation).
• Analyzing transcriptional defects using reporter assays.
• Co-immunoprecipitation experiments to study protein interactions.

Main Results:

• Overexpression of RPB7 suppressed the temperature-sensitive growth defect of rpb4Delta cells at 34°C.
• RPB7 overexpression partially rescued cold sensitivity and fully rescued starvation sensitivity.
• Overexpression of RPB4 did not rescue the essentiality of RPB7.
• RPB7 overexpression suppressed transcriptional defects in rpb4Delta cells under mild heat shock.
• Rpb4 augments the interaction of Rpb7 with Pol II, with less Rpb7 interacting with Pol II lacking Rpb4.

Conclusions:

• Rpb4's major role is to enhance Rpb7's stable association with Pol II.
• Yeast Pol II lacking Rpb4 (Pol IIDelta4) has a limited amount of Rpb7, sufficient only for non-stress conditions.
• Overexpression of RPB7 increases its assembly with Pol IIDelta4, enabling transcription under certain stress conditions.