Multiple endocrine neoplasia types 2A and 2B (MEN2A and MEN2B) and familial medullary thyroid carcinoma are dominantly inherited cancer syndromes. All three syndromes are associated with mutations in RET, which encodes a receptor-like tyrosine kinase. The altered RET alleles were shown to be transforming genes in NIH 3T3 cells as a consequence of constitutive activation of the RET kinase. The MEN2A mutation resulted in RET dimerization at steady state, whereas the MEN2B mutation altered RET catalytic properties both quantitatively and qualitatively. Oncogenic conversion of RET in these neoplastic syndromes establishes germline transmission of dominant transforming genes in human cancer.

The interaction between the U1 snRNP‐specific U1 A protein and U1 snRNA has been analysed. The binding site for the protein on the RNA is shown to be in hairpin II, which extends from positions 48 to 91 in the RNA. Within this hairpin the evolutionarily conserved loop sequence is crucial for interaction with U1 A protein. U1 A protein can also bind the loop sequence when it is part of an artificial RNA which cannot form a stable hairpin structure. The region of the protein required to bind to U1 snRNA consists of a conserved 80 amino acid motif, previously identified in many ribonucleoprotein (RNP) proteins, together with (maximally) 11 N‐terminal and 10 C‐terminal flanking amino acids. Point mutations introduced into two of the most highly conserved regions of this motif abolish RNA binding. U1 snRNA mutants from which the U1 A binding site has been deleted are shown to be capable of assembly into RNP particles which are immunoprecipitable by patient antisera which recognize U1 A protein. The role of RNA‐protein and protein‐protein interactions in U snRNP assembly are discussed.

The basis of the specificity of interaction of U1 and U2 small nuclear (sn)RNAs and their cognate binding proteins, U1A and U2B'', has been examined. The U1A protein recognizes U1 snRNA on its own, whereas U2B'' binds specifically to U2 snRNA only in the presence of a second protein, U2A'. Exchange of two nucleotides between the two RNAs or of eight amino acids between the two proteins reverses binding specificity.

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Muscle actin genes are the earliest yet described to show cell type-specific activation in amphibian embryos. Gene-specific probes show that alpha-skeletal and alpha-cardiac actin genes start to be transcribed simultaneously at the end of gastrulation, but only in those regions of the mesoderm that subsequently form embryonic muscle. Their expression provides a molecular marker for early cell determination.