Question

A hypothetical family of proteins consists of six similar but different proteins. Each of the six proteins can form transcription factors by forming homo- or heterodimers in combinatorial mixtures, each binding to different regulatory sites. Calculate the number of different dimeric structures that can be formed from the six proteins (and, thus potential number of different regulatory sites that can be bound). Show the calculation.

Answer 1

Since the family consists of 6 proteins each of which can form a homodimer or a heterodimer, each protein in this family can potentially bind 6 proteins: itself and the 5 other proteins in this family. Therefore, if there are 6 proteins, A, B, C, D, E, and F then the various combinations would be AA, AB, AC, AD, AE, AF, BB, BC, BD, BE, BF, CC, CD, CE, CF, DD, DE, DF, EE, EF, and FF. This means there are 21 unique dimers that can be formed with this family of proteins.