Well M is meaningless in this case since the "UP" indicates this is a first-for-coach instant upgrade type fare so the booking class is going to be different from the first letter of the fare basis code.

Does the "A" indicate the true booking class of A? Possibly. Although other carriers' .UP fares don't use this convention.

The "00" likely advance purchase; in this case zero. So this is a walkup fare (subject, of course, to the inventory being available).

The "R" likely indicates refundable. An "N" in this position would normally indicate a non-refundable fare.

As for the terminating "J" this is pure speculation but it could have some internal meaning within DL Pricing in terms of alerting them to which pricing structure group it falls under (specific LCC fare structures, surcharge applicability, etc.)