30. Following statements were made about catalytic introns:
A. Group I introns may undergo self-splicing by transesterification.
B, Group II introns do not require any factor/protein for auto-splicing either in vivo or in vitro
C. Certain introns of both the group I and II classes may contain open reading frames which are translated into protein.
D. Generally, group I introns migrate by DNA mediated mechanisms, whereas group II introns migrate by RNA-mediated mechanisms.
E. Ribonuclease P (RNase P) is essential for bacteria and archaea but not eukaryotes.
Which one of the following combinations represents statements which are all correct?
(1) A, B, D             (2) B, D, E
(3) A, C, D             (4) C, D, E

The correct combination of statements that are all true about catalytic introns is:

(3) A, C, D

Explanation of Each Statement:

A. Group I introns may undergo self-splicing by transesterification.
True. Group I introns self-splice via two sequential transesterification reactions initiated by an exogenous guanosine cofactor that attacks the 5′ splice site, leading to intron excision and exon ligation.

B. Group II introns do not require any factor/protein for auto-splicing either in vivo or in vitro.
False. Although group II introns are self-splicing ribozymes capable of catalyzing their own excision in vitro, in vivo splicing efficiency often requires protein cofactors (maturases) for proper folding and catalysis. Hence, this statement is not fully correct.

C. Certain introns of both the group I and II classes may contain open reading frames which are translated into protein.
True. Many group I and group II introns harbor open reading frames (ORFs) encoding homing endonucleases or maturase proteins that assist intron mobility or splicing.

D. Generally, group I introns migrate by DNA mediated mechanisms, whereas group II introns migrate by RNA-mediated mechanisms.
True. Group I introns often spread via homing endonuclease-mediated DNA recombination (DNA-mediated mobility), while group II introns can act as retroelements, moving via RNA intermediates and reverse splicing into DNA (RNA-mediated mobility).

E. Ribonuclease P (RNase P) is essential for bacteria and archaea but not eukaryotes.
False. RNase P is essential in all domains of life, including bacteria, archaea, and eukaryotes, as it processes the 5′ ends of tRNA precursors. Thus, this statement is incorrect.

Summary Table

Conclusion

The only fully correct combination is (3) A, C, D.