In the absence of hormone, TR forms a complex with corepressor proteins such as nuclear receptor co-repressor 1 (N-CoR) and 2 (N-CoR2). While these cofactors are present, TR binds HREs in a transcriptionally inactive state. This inhibition of gene transcription allows for tight regulation of gene products. Binding of thyroid hormone results in a conformational change in helix 12 of the TR transactivation domain, which displaces the corepressors from the receptor/DNA complex. Coactivator proteins are recruited, forming a DNA/TR/coactivator complex. One coactivator recruited to the site is nuclear receptor co-activator 1 (NCoA-1). RNA polymerase is recruited to the site and transcribes downstream DNA into messenger RNA (mRNA). The mRNA generated is then translated into the corresponding proteins. The protein products from this process drive the changes in cell function observed in the presence of thyroid hormone.