T7 promoter: Drives high-level transcription of the gene of interest when T7 RNA polymerase is present. When placed immediately upstream of a LacO element, the entire cassette is known as the T7lac promoter.
LacO: Binding site for LacI. This element inhibits activity of the T7 promoter when LacI protein is present, preventing leaky expression of the gene of interest.
RBS: The ribosome-binding site and translation initiation element from T7 bacteriophage. This allows for efficient production of the protein of interest.
ORF: The open reading frame of your gene of interest is placed here.
T7 terminator: Signal sequence to terminate the transcript made from the gene of interest, preventing run-on transcription.
Ampicillin: Ampicillin resistance gene. It allows the plasmid to be maintained by ampicillin selection in E. coli.
pBR322 ori: pBR322 origin of replication. Plasmids carrying this origin as well as the Rop gene exist in low copy numbers in E. coli.
Rop: Repressor of primer. It encodes a small protein that regulates plasmid copy number. The presence of the Rop protein, in combination of pBR322 origin of replication on the plasmid, results in low copy numbers of the plasmid.
LacI: The E. coli natural promoter and coding sequence for the lac repressor. In the absence of induction of the system (i.e. without IPTG), the LacI protein represses transcription of the gene of interest from the T7lac promoter, as well as transcription of T7 RNA polymerase from the LacUV5 promoter in host strains used for recombinant protein production.