Endonuclease involved in 16S rRNA intron I-alpha homing. Recognizes the minimal target 5'-GCAAGGCTGAAACTTAAAGG-3'; generates 4 base 3' protruding ends 5'-AAAC-3' and 5'-GTTT-3'. 1-5 mM manganese gives higher cleavage activity than the same concentration of magnesium. Optimum pH is 7.5. Optimum temperature is 90 degrees Celsius. Active from 70 to 90 degrees Celsius. Probably functions as a monomer.