If you wanted a crash course in genetics, this is certainly a great question for it. Let me see if I can explain it, or at least break it down for you. Of course you probably know that the B-RAF is a proto-oncogene, and its job is to produce a protein that will signal a nearby cell to grow or replicate. There are many mutations in a gene, and these mutations occur along the long chain of DNA. The chain of DNA is comprised of nucleotides and amino acids. The nucleotides are (A) Adenine, (G) Guanine, (C) Cytosine, and (T)Thymine ((U) Uracil in RNA). They are in sequences called codons which are three nucleotides that form a genetic code. In a DNA chain there are introns which are like spacers in between the codons that do not code for anything, then there are exons which carry codes for the placement of amino acids and protiens along the chain to enhance the nucleotides; kind of like the instructions for the recipe of you, which amino acid codons to combine and when/where, etc. B-RAF is a point mutation, and this is a mutation that changes only one small area, or one nucleotide in a gene, like a T to A exchange, or an exchange of an amino acid. With nucleotides, T always lines up with A, and C always lines up with G. There are different types of mutations like a missense, nonsense, frameshift, or silent mutations, however I won't get into that (a bit dry) here. Now to explain K601N.
The B-RAF gene can mutate in many ways, and does mutate in many, many ways. One popular mutation is the V600E mutation along the B-RAF Mutations. Of the 21 or 22 amino acids in the body (each has a letter symbol & abbreviation) V=the amino acid Valine, and E= the amino acid called Glutamic acid. V was substituted for E at the 600th codon. You have the point mutation of K601N, K= the amino acid Lysine, and N= the amino acid Asparagine, and it occured at the 601 codon. It seems like a lot of codons but a strand of DNA is quite long so at one point in your strand, at the point of the 601 codon, Lysine was substituted for Asparagine.
Your doc is right that you would be hard pressed to find any article on this mutation, it is a subtype of another mutation. The V600E mutation is associated with a disease like Hairy Cell Leukemia. K601N is associated with Melanoma and B-Raf mutations in Melanoma seem to react off of exposure to intermediate UV light.
I apoligize if this was a boring lesson but I hope that I have at least explained it in a way that makes sense. This was the way it was explained to me when I studied genomics, and it was easier for me to understand it when explained to me in this fashion. I hope this helps you somehow, Carm RN.