S-adenosyl-L-methionine-dependent methyltransferase that adds a methylphosphate cap at the 5'-end of 7SK snRNA, leading to stabilize it (By similarity). Required for dorso-ventral patterning in oogenesis and for anterior-posterior pattern formation during embryogenesis, possibly by binding and stabilizing 7SK RNA, thereby promoting formation of a repressive RNA-protein complex (PubMed:21262214). a 5'-end triphospho-guanosine-ribonucleotide-snRNA + S-adenosyl-L-methionine = a 5'-end methyltriphosphate-guanosine-ribonucleotide-snRNA + S-adenosyl-L-homocysteine Interacts with bicoid/bcd. Distributed throughout the early embryo. Detectable in early embryos. Present coincident with bicoid/bcd expression, with peak levels detected in 0-2 hours embryos. Expression is lower during cellularization stages (2-4 hours) and drops dramatically during late embryonic development (4-24 hours). Very little, if any expression is detected in unfertilized eggs. Severe defect in oogenesis: females lay eggs, however, up to 50% do not initiate development and many show a dorsalized phenotype. Among the eggs that do initiate development, up to 20% fail to complete embryogenesis and of these, nearly all display severe head defects and die as unhatched larvae or die soon after hatching. Mutants show anterior pattern defects and fail to repress the translation of caudal mRNA and exhibit head involution defects. Mutants also display a severe reduction in the level of 7SK RNA and reduced binding of bicoid/bcd to the caudal 3' UTR. Belongs to the methyltransferase superfamily.