Putative HNH endonuclease component of antiviral defense system retron Ec83, composed of a non-coding RNA (ncRNA), a reverse transcriptase (RT), a probable ATPase and this protein. Expression of retron Ec78 confers protection against bacteriophage T2, T4 and T6. At multiplicity of infection (MOI) of 0.02 cultures slow growth when infected with T4 but do not collapse, at MOI 2 cultures enter growth stasis.