Carbohydrate sulfotransferase 15, also known as N-acetylgalactosamine 4-sulfate 6-O-sulfotransferase, GalNAc4S-6ST, B-cell RAG-associated gene protein, CHST15 and BRAG, is a single-pass type I I membrane protein which belongs to the sulfotransferase 1 family. CHST15 / BRAG is expressed in B-cell-enriched tissues but not in fetal or adult thymus. It is expressed in fetal and adult spleen, lymph node, tonsil, bone marrow and peripheral leukocytes. It is not expressed in T-cells. In pro-B, pre-B, and mature B-cell lines, it colocalizes with RAG1. CHST15 / BRAG is a sulfotransferase that transfers sulfate from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to the C-6 hydroxyl group of the GalNAc 4-sulfate residue of chondroitin sulfate A and forms chondroitin sulfate E containing GlcA-GalNAc(4,6-SO4) repeating units. It also transfers sulfate to a unique non-reducing terminal sequence, GalNAc(4SO4)-GlcA(2SO4)-GalNAc(6SO4), to yield a highly sulfated structure similar to the structure found in thrombomodulin chondroitin sulfate. CHST15 / BRAG may also act as a B-cell receptor involved in BCR ligation-mediated early activation that mediate regulatory signals key to B-cell development and / or regulation of B-cell-specific RAG expression.