public void EnsureKey(MapLink link, TssRegulatoryMap tssMap)
        {
            if (!tssMap.ContainsKey(link.TranscriptName))
            {
                tssMap.Add(link.TranscriptName, new Dictionary <MapLink.Locus, MapLink>());
            }

            if (tssMap[link.TranscriptName].ContainsKey(link.LocusName))
            {
                throw new Exception(string.Format("Duplicate Locus-TSS link {0}-{1} in map", link.LocusName, link.TranscriptName));
            }
        }