3'-5' RNA helicase that plays a key role in the male and female germline by promoting transition from mitotic to meiotic divisions in stem cells (PubMed:28380054, PubMed:28809393, PubMed:29033321, PubMed:29087293, PubMed:29360036, PubMed:32470506). Specifically recognizes and binds N6-methyladenosine (m6A)-containing RNAs, a modification present at internal sites of mRNAs and some non-coding RNAs that plays a role in the efficiency of RNA processing and stability (PubMed:29360036). Essential for ensuring a successful progression of the meiotic program in the germline by regulating the level of m6A-containing RNAs (PubMed:29033321). Acts by binding and promoting degradation of m6A-containing mRNAs: the 3'-5' RNA helicase activity is required for this process and RNA degradation may be mediated by XRN1 exoribonuclease (PubMed:29033321). Required for both spermatogenesis and oogenesis (PubMed:28809393, PubMed:29033321). ATP + H2O = ADP + H(+) + phosphate Interacts with MEIOC; binds transcripts that regulate the mitotic cell cycle inhibiting progression into metaphase, thereby allowing meiotic prophase to proceed normally (PubMed:28380054, PubMed:29087293). Interacts (via ANK repeats) with XRN1 (By similarity). Interacts with ZCCHC4 (By similarity). Associates with the small ribosomal subunit (By similarity). Present in male and female germ cells (at protein level) (PubMed:29033321, PubMed:32470506). Highly expressed in testis (PubMed:28809393, PubMed:29033321, PubMed:29087293, PubMed:29360036). Not detected in spermatogonia next to the tubule wall but is strongly expressed in spermatocytes, suggesting that it is up-regulated in germ cells upon entry into meiosis (at protein level) (PubMed:29087293). Expression rises between 7 and 12 d.p.p. and remains steady through adulthood. The YTH domain mediates RNA-binding. It recognizes and binds N6-methyladenosine (m6A)-containing RNAs. Mice are viable and reach adulthood (PubMed:28809393, PubMed:29087293, PubMed:29033321). However, both male and female mice are infertile; male mice have smaller testes, and female mice have smaller ovaries and show progressive loss of germ cells (PubMed:28809393, PubMed:29087293, PubMed:29033321). Mutant germ cells enter meiosis but proceed prematurely to aberrant metaphase and apoptosis, and display defects in transitioning from spermatogonial to meiotic gene expression programs (PubMed:29087293, PubMed:29033321). Mutant testes reveal an up-regulation of N6-methyladenosine (m6A)-enriched transcripts (PubMed:29033321). 'Ketu' is a harbinger of misfortune in Vedic mythology (PubMed:29360036). Belongs to the DEAD box helicase family. DEAH subfamily.