different effects on transcription, with some, such as c -jun, being more 
positively acting and others, such as jun-B , tending to be more negatively 
acting (Bohmann et al. 1987; Chiu et al. 1988, 1989; Nakabeppu and Nathans 
1991; Schonthal et al. 1989; Schutte et al. 1989). In addition, many of these 
complexes can be modified posttranslationally, especially by phosphorylation, 
and these phosphorylations can affect the function of the complex (Barber and 
Verma 1987; Boyle et al. 1991 ; Lamph et al. 1990; Ofir et al. 1990; Binetruy 
et al. 1991). Thus, through combinatorial action, the fos/jun gene family can 
potentially exert a broad range of effects on the transcriptional program of the 
cell. 
However, the fos/jun family are not the only transcription factors that are early- 
response genes. Other early-response genes that appear to be transcription 
factors are z/77268, which encodes a zinc finger protein (Christy et al. 1988); 
nur77, which is related to the steroid receptor family of transcription factors 
(Hazel et al. 1988; Milbrandt 1988); and the c-mycgene, which has both a 
helix-loop-helix domain and a leucine zipper (Murre et al. 1989). All these 
genes are likely to be involved in the regulation of late-response genes, which 
then presumably alter physiology and function of the cell. Secreted proteins 
that are lEGs are KC/gro, which appears to be a melanocyte growth factor 
(Anisowicz et al. 1987; Richmond et al. 1988), and JE, which is a member of a 
large family of monocyte chemotractant factors (Oquendo et al. 1989; Rollins et 
al. 1989). The functions of these secreted factors are not specific to fibroblasts 
because expression of JE and KC has been detected in monocytes (Orlofsky 
and Stanley 1987). 
In addition to studies on fibroblasts, investigators have cloned genes from 
other cell types that are induced early in response to various growth and 
differentiation stimuli. Typically, it has been found that many of the genes 
induced in T cells by mitogens, in liver cells by partial hepatectomy, or by 
nerve growth factor (NGF) in PCI 2 cells are the same ones that are induced 
by PDGF in 3T3 cells (Greenberg et al. 1985; Kujubu et al. 1987; Thompson 
et al. 1986; Zipfel et al. 1989). Genes that are commonly induced in many 
different cell types by many different agents typically include c-fbs, c -jun, and 
the c-myc proto-oncogenes (Bartel et al. 1989; Greenberg et al. 1985; Kelly et 
al. 1983; Mechta et al. 1989; Thompson et al. 1986). In addition, in each cell 
type there appears to be a class of early-response genes that have a pattern 
of expression restricted to a particular cell type. For instance, in activated T 
cells, there is a rapid induction of interleukin-2 (IL-2) and its receptor, both of 
which are gene products that are specifically expressed in T cells (Greene et 
al. 1989; Taniguchi 1988). Similarly, in PCI 2 cells there are unique cytoskeletal 
proteins that are induced early in the response to NGF (Leonard et al. 1988). 
6 
