The venom-gland transcriptome of Micrurus fulvius was extremely biased towards toxin production. The venom-gland transcriptome of M. fulvius was dominated by toxin transcripts and, in particular, phospholipases A2 (PLA2s). (A) A total of 1,950 nontoxin-encoding and 116 toxin-encoding transcripts were identified. Toxins were grouped into 75 clusters based on <1% nucleotide divergence. The inset shows a magnification of the top 200 transcripts, the vast majority of which code for toxins. (B) Expression levels of individual toxin clusters, color coded by toxin class. The 75 toxin clusters represent 15 distinct toxin classes. Three-finger toxin and PLA2 transcripts dominated toxin expression levels, accounting for nearly 86% of all toxin reads. Toxin-class abbreviations are as follows: 3FTx: three-finger toxin; CTL: C-type lectin; CREGF: cysteine-rich with EGF-like domain; HYAL: hyaluronidase; KUN: Kunitz-type protease inhibitor; LAAO: L amino-acid oxidase; LCN: long-chain neurotoxin; NGF: nerve growth factor; NP: natriuretic peptide; NUC: nucleotidase; PDE: phosphodiesterase; PLA2: phospholipase A2; PLB: phospholipase B; SVMP: snake venom metalloproteinase; VEGF: vascular endothelial growth factor.