A leucine zipper is a type of protein structure that plays a crucial role in the regulation of gene expression. It consists of a series of leucine amino acids spaced at regular intervals, allowing two protein chains to dimerize, or bind together. This dimerization is essential for the protein's ability to attach to DNA and influence transcription. Leucine zippers are commonly found in various transcription factors, which are proteins that help control the flow of genetic information from DNA to RNA. Examples of these transcription factors include c-Fos and c-Jun, which are involved in cellular processes like growth and differentiation.