Transcription producing tRNA. Illustration of a strand of DNA (deoxyribonucleic acid, blue) undergoing transcription to produce molecules of transfer ribonucleic acid (tRNA). These relatively small nucleic acid fragments are part of the process used in the cellular synthesis of proteins. They are typically 76 to 90 nucleotides in length and form a twisted four-pronged 'cloverleaf' structure. The production of tRNA and other small RNAs is carried out by an enzyme complex called RNA polymerase III.