Regulatory subunit of calcineurin, a calcium-dependent, calmodulin stimulated protein phosphatase (PubMed:11352578). Confers calcium sensitivity (PubMed:11352578). Important for stalk formation (PubMed:16512895). Forms a complex composed of a calmodulin-dependent catalytic subunit canA (also known as calcineurin A) and a regulatory Ca(2+)-binding subunit cnbA (also known as calcineurin B). Isoform 1 is present in constant amounts in vegetative cells and throughout development. Isoform 2 is barely detectable in vegetative and early preaggregative cells, but present at high levels during aggregation and in later stages (at protein level). Amoeba with reduced cnbA levels produce smaller stalk cells and smaller stalks due to incomplete vacuolization of stalk cells. Belongs to the calcineurin regulatory subunit family.