It’s revealing what @stcordova chooses to omit. Let’s lend a hand (note that I will use very round numbers here and may toggle between nts and bp - this is to make the post easy to write and read):
From https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5199132/:
The total number of introns in protein-coding genes = 134,497 (non-redundant)
total intron length = 9.4x10^8 bp (non-redundant)
In long-non-coding RNAs, the total number of introns = 21,297
Intron length in these = 2.1x10^8 bp
Thus, total intron length = 1.1x10^9 bp (approximately)
Every intron has a core of some 20 nts that is needed for splicing. This adds up to 3x10^6 bp of function.
If every intron has an enhancer that binds 5 transcription factors, and if every TF binds a 10 nt sequence, this gives us about 8x10^6 bp of functionality.
If every intron binds five splicing regulators, and each of these binds 10 nts of RNA, then we have another 8x10^6 bp of functionality.
Sternberg mentions 1664 microRNAs and 717 stable RNAs (snRNAs, snoRNAs). Generously, there will be 10^7 bp of functionality in these two groups (combined). (This is a wild overestimate – in reality, these classes of RNA contribute less than 0.1% of all intronic sequences).
Sternberg mentions 78,147 intron-derived non-coding RNAs. The paper he cites is old and draws from EST sequences, so it is not clear how many of these are “real”. However, the authors of the study note that:
“An overlapping tissue expression signature was detected for both species, comprising 198 transcripts; among these, 22 RNAs map to intronic regions with evidence of evolutionary conservation in humans and mice.”
So most of these may not be authentic. However, let’s say that all 78,000 or so have some function, mediated by binding to proteins. If each one binds 10 proteins (a very generous assumption), and each protein binds to a 10 nt motif, then each RNA would have 100 nts of functionality. This gives us 8x10^7 bp of functionality.
Adding these things up, then we come up with an estimate of some 10^8 bp of functionality. I would point out that I have made assumptions that are tremendously favorable to @stcordova – all introns don’t have enhancers, and all introns won’t bind splicing regulators, and intronic RNAs won’t all have function or bind so many proteins. Even when granting all of these things, we can see that less than 10% of all intronic sequences might be functional.
It’s pretty hard to see how one gets from this to the claims by IDists (like Sternberg and Wells) that 80% or more of intronic sequences are functional.