Novel precursor mirna and application thereof in tumor treatment

A precursor sequence, characterised in that the sequence has a structure from the 5′ terminus to the 3′ terminus as shown in formula I:

• wherein B1 is a first ribonucleic acid sequence as desired, and comprises an anti-miRNA sequence form or an siRNA sequence form;
• B2 is a sequence substantially or completely complementary to B1, and B2 is not complementary to C;
• C is a stem-loop structure sequence;
• and
• A1 and A2 are null or are optionally RNA sequences consisting of 4-5 bases respectively;
• wherein the precursor can express (or produce or enrich) the first ribonucleic acid sequence in a host, but cannot express (or produce or enrich) a second ribonucleic acid sequence complementary to the first ribonucleic acid sequence.