The main job for North Turrets is to help keep Tequatl's Scales from reaching 20 and creating a Bone Wall, which will make him invulnerable until it is removed.
They also are responsible for cleansing on the North side of the map. This includes North Hills, North Turrets themselves, and very rarely North Boat.
To remove Tequatl's Scales, the turrets need to target Teq's head and press 2. This should be done immediately once the ability is off of cooldown (CD).
Buffs are also available as well as cleansing, which clears the poison AoE, on 3-5.
T4-T6, or North Turrets, is often considered to be the easier of the two turret positions.