http://www.mirror.co.uk/news/uk-news/uks-smoking-capital-revealed-how-6759245Day 187 has 18 protein-coding genes (browser view) including CHRNB3 (Neuronal acetylcholine receptor subunit beta-3).
This gene encodes part of a nACHr, whose natural job in the brain is to respond to a neurotransmitter, but which can also be turned on by nicotine.
Click here to see all 8537567 letters of Day 187 with CHRNB3