Perfect match calculation

There are approximately 500 small RNAs in P. aeruginosa (⁷⁵) with an average length of 188 nt, constituting a total of ~86,000 16-nt windows within these small RNAs. The length of the maco-1 coding sequence is approximately 2700 nucleotides, and so contains ~1,350 semi-independent 16-nt windows (allowing up to 90% overlap between neighboring 16-nt windows). The product of these two numbers is ~116,100,000 pairs of potentially matching windows. Dividing by 4^16 possible 16-nt sequences yields an estimated probability of ~0.027. It should be noted that this number is likely an overestimate, as it assumes that the 86,000 windows in the small RNAs are independent of one another, which is not the case.