ABSTRACT
UUU or UUC Phenylalanine UAA orUAG Nonsense (ochre)
Nonsense (amber) UUA or UUG Leucine CAU or CAC Histidine CUU, CUC, CUA, or CUG Leucine CAA or CAG Glutamine AUU, AUC, or AUA Isoleucine AAU or AAC Asparagine AUG Methionine AAA or AAG Lysine GUU, GUC, GUA, or GUG Valine GAU or GAC Aspartic acid UCU or UCC Serine GAA or GAG Glutamic acid UCA or UCG Serine UGU or UGC Cysteine CCU, CCC, CCA, or CCG Proline UGA Nonsense (umber) ACU, ACC, ACA, or ACG Threonine CGU, CGC, CGA, or
CGG Arginine
GCU, GCC, GCA, or GCG Alanine AGU or AGC Serine UAU or UAC Tyrosine AGA or AGG Arginine
GGU, GGC, GGA, or GGG
Glycine
Initiation Promotion Progression
• Irreversible • Reversible • Irreversible • Additive • Nonadditive • Karyotypic
abnormalities appear accompanied by increased growth rate and invasiveness
• Dose response can be demonstrated; does not exhibit a readily measurable threshold
• Dose response having a measurable threshold can be demonstrated
• Benign and/or malignant tumor observed
• No measurable maximum response
• Measurable maximum effect
• Environmental factors influence early stage of progression
• Initiators are usually genotoxic
• Promoters are usually not mutagenic
• Progressors may not be initiators
• One exposure may be sufficient
• Prolonged and repeated exposure to promoters required
• Progressors act to advance promoted cells to a potentially malignant stage
• Must occur prior to promotion
• Promoter effective only after initiation has occurred
• Spontaneous progression can occur
• Requires fixation through cell division
• Promoted cell population dependent on continued presence of promoter
• Initiated cells are not identifiable except as foci lesions following a period of promotion
• Causes expansion of the progeny of initiated cells, producing foci lesions
• “Pure” initiation does not result in neoplasia without promotion
• “Pure” promoters not capable of initiation
• Spontaneous (fortuitous) initiation can occur
• Sensitive to hormonal and dietary factors
Source: Adapted from Pitot, H.C. (1991) and Maronpot, R.R. (1991).
