Fill in each blank with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once. translation sigma factor stop codon promoter DNA polymerase pause site tmRNA transcription ribosome attenuation RBS RNA polymerase Rho factor start codon tRNA The first step in gene expression is by to make an mRNA that encodes for one or more proteins. This requires that a binds to the DNA at the sequence upstream of the open-reading-frame. A protein is then made by of an mRNA by the . Termination of transcription requires a while termination of translation requires a . An antisense sRNA can inhibit translation initiation through complementary base-pairing to the sequence in its target mRNA. Transcription of the trp operon is repressed when tryptophan levels are abundant and the cell is able to make charged s with this amino acid. Ribosomes that are stalled on an mRNA that lacks a stop codon are rescued by a that encodes a tag that targets the protein for degradation followed by a stop codon.