Methylase methylates DNA, making the DNA resistant to restriction endonucleases

*https://d2jmvrsizmvf4x.cloudfront.net/7Pf4zZ3TuGwLTRKvUGYL_methylatedrestriction.jpg

Explanations for this are too complicated. Think of it like this:

You've got a piece of mutated DNA that is able to be digested by a restriction endonuclease, that means the DNA was transcriptionally available to begin with. AKA it was not methylated, because as we know, methylation = heterochromatin which is transcriptionally inactive. that means methylase was mutated

Only other plausible answer was DNase, and if it was mutated it would be inactive, not overactive.

In prokayotes Normally methylase adds methyl group to certain base(adenine) so restriction endonuclease can not recognize this site. If there is a mutation in methylase enzyme it can't add methyl group to adenine so restriction endonuclease can recognize it and can cleave it.

My thought process for this one: In DNA mismatch repair for bacteria there is a parent strand and a newly synthesized strand. The parent strand is methylated prior to replication to allow it to be differentiated from the new strand in the case of mismatching. The new strand is identified by the lack of methylation and then degraded by endonucleases. So I used this logic to think altered methylase (decreased activity) allows for more DNA to be degraded by endonucleases. Not sure if its the best logic but it got me there lol

Resistant to digestion: does not break or get deactivated (endonuclease creates a nick in the strand, which means that it BREAKS the strand; even if it is for correction purposes) Deactivation is done by methylation; so if methylase is defective, the sequence will never be muted (digested/ broken down/ cleaved)