Transcription factor and ribosomal RNA (rRNA). Molecular model showing the 6 zinc fingers of transcription factor IIIA (magenta) bound to RNA (ribonucleic acid, orange and cyan) from a 5s ribosome sub-unit. Transcription factors are proteins that bind to specific DNA sequences, and control the movement (transcription) of genetic information from DNA to mRNA (messenger RNA) during gene expression. Ribosomes are responsible 'reading' the RNA strand and assembling amino acids to form the protein encoded by the gene being 'read'.