Trans-acting
In the field of molecular biology, trans-acting, in general, means "acting from a different molecule". It may be considered the opposite of cis-acting, which, in general, means "acting from the same molecule".
In the context of transcription regulation, a trans-acting factor is usually a regulatory protein that binds to DNA. The binding of a trans-acting factor to a cis-regulatory element in DNA can cause changes in transcriptional expression levels. microRNAs or other diffusible molecules are also examples of trans-acting factors that can regulate target sequences.
The trans-acting gene may be on a different chromosome to the target gene, but the activity is via the intermediary protein or RNA that it encodes. Cis-acting elements, on the other hand, do not code for protein or RNA. Both the trans-acting gene and the protein/RNA that it encodes are said to "act in trans" on the target gene.
