A protein involved in assisting E.coli RNA polymerase to terminate  transcription at certain terminators is called  

A protein involved in assisting E.coli RNA polymerase to terminate  transcription at certain terminators is called  rho factor.

Release factor is a protein that binds to the ribosome during translation and helps to release the completed protein from the ribosome.

Sigma factor is a protein that binds to the RNA polymerase and helps to initiate transcription by recognizing specific promoter sequences.

Elongation factor is a protein that helps the ribosome to move along the mRNA and add amino acids to the growing protein during translation.