What type of RNA is known for regulating transcription?

MicroRNA is a small non-coding RNA molecule that plays a crucial role in the regulation of transcription and post-transcriptional processes. It functions by binding to complementary sequences on messenger RNA (mRNA) and can either lead to mRNA degradation or inhibit its translation into protein. This regulation is important for various cellular processes, including development, differentiation, and response to environmental signals.

In contrast, ribosomal RNA (rRNA) is primarily involved in the structural and functional components of ribosomes, where protein synthesis occurs, rather than regulating transcription. Messenger RNA (mRNA) serves as the intermediary that conveys genetic information from DNA to the ribosomes for protein synthesis but does not regulate transcription itself. Small nuclear RNA (snRNA) is involved in mRNA processing and splicing but does not directly regulate transcription either.

Thus, microRNA is specifically recognized for its capacity to regulate gene expression at the transcription and translation levels, making it the correct choice for this question.