In molecular biology

Molecular biology

Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

, HOTTIP (HOXA transcript at the distal tip) is a long non-coding RNA. The gene encoding HOTTIP is located at the 5' tip of the HOXA locus, and coordinates the activation

Regulation of gene expression

Gene modulation redirects here. For information on therapeutic regulation of gene expression, see therapeutic gene modulation.Regulation of gene expression includes the processes that cells and viruses use to regulate the way that the information in genes is turned into gene products...

 of several of the 5' HOXA genes. The non-coding RNA is brought into close proximity with the HOXA genes by chromosomal looping. HOTTIP binds to the WDR5

WDR5

WD repeat-containing protein 5 is a protein that in humans is encoded by the WDR5 gene.-Interactions:WDR5 has been shown to interact with Host cell factor C1 and MLL. It also interacts with the long non-coding RNA HOTTIP.-Further reading:...

 protein, which forms a complex with the histone methyltransferase

Histone methyltransferase

Histone methyltransferases are enzymes, histone-lysine N-methyltransferase and histone-arginine N-methyltransferase, that catalyze the transfer of one to three methyl groups from the cofactor S-Adenosyl methionine to lysine and arginine residues of histone proteins...

 protein MLL

MLL (gene)

Histone-lysine N-methyltransferase HRX is an enzyme that in humans is encoded by the MLL gene.MLL is a histone methyltransferase deemed a positive global regulator of gene transcription...

. This targets the WDR5-MLL complex to the HOXA region and results in H3K4 methylation and transcriptional activation of the HOXA locus.